The Tor Browser: browser/devtools/shared/widgets/ViewHelpers.jsm@6474c204b198 (annotated)

browser/devtools/shared/widgets/ViewHelpers.jsm@6474c204b198 (annotated)

browser/devtools/shared/widgets/ViewHelpers.jsm

Wed, 31 Dec 2014 06:09:35 +0100

author: Michael Schloh von Bennewitz <michael@schloh.com>
date: Wed, 31 Dec 2014 06:09:35 +0100
changeset 0: 6474c204b198
permissions: -rw-r--r--

Cloned upstream origin tor-browser at tor-browser-31.3.0esr-4.5-1-build1
revision ID fc1c9ff7c1b2defdbc039f12214767608f46423f for hacking purpose.

 /* -*- Mode: javascript; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
 /* vim: set ft=javascript ts=2 et sw=2 tw=80: */
 /* This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 "use strict";
 const Cc = Components.classes;
 const Ci = Components.interfaces;
 const Cu = Components.utils;
 const PANE_APPEARANCE_DELAY = 50;
 const PAGE_SIZE_ITEM_COUNT_RATIO = 5;
 const WIDGET_FOCUSABLE_NODES = new Set(["vbox", "hbox"]);
 Cu.import("resource://gre/modules/Services.jsm");
 Cu.import("resource://gre/modules/XPCOMUtils.jsm");
 Cu.import("resource://gre/modules/Timer.jsm");
 Cu.import("resource://gre/modules/devtools/DevToolsUtils.jsm");
 this.EXPORTED_SYMBOLS = [
   "Heritage", "ViewHelpers", "WidgetMethods",
   "setNamedTimeout", "clearNamedTimeout",
   "setConditionalTimeout", "clearConditionalTimeout",
 ];
 /**
  * Inheritance helpers from the addon SDK's core/heritage.
  * Remove these when all devtools are loadered.
  */
 this.Heritage = {
   /**
    * @see extend in sdk/core/heritage.
    */
   extend: function(aPrototype, aProperties = {}) {
     return Object.create(aPrototype, this.getOwnPropertyDescriptors(aProperties));
   },
   /**
    * @see getOwnPropertyDescriptors in sdk/core/heritage.
    */
   getOwnPropertyDescriptors: function(aObject) {
     return Object.getOwnPropertyNames(aObject).reduce((aDescriptor, aName) => {
       aDescriptor[aName] = Object.getOwnPropertyDescriptor(aObject, aName);
       return aDescriptor;
     }, {});
   }
 };
 /**
  * Helper for draining a rapid succession of events and invoking a callback
  * once everything settles down.
  *
  * @param string aId
  *        A string identifier for the named timeout.
  * @param number aWait
  *        The amount of milliseconds to wait after no more events are fired.
  * @param function aCallback
  *        Invoked when no more events are fired after the specified time.
  */
 this.setNamedTimeout = function setNamedTimeout(aId, aWait, aCallback) {
   clearNamedTimeout(aId);
   namedTimeoutsStore.set(aId, setTimeout(() =>
     namedTimeoutsStore.delete(aId) && aCallback(), aWait));
 };
 /**
  * Clears a named timeout.
  * @see setNamedTimeout
  *
  * @param string aId
  *        A string identifier for the named timeout.
  */
 this.clearNamedTimeout = function clearNamedTimeout(aId) {
   if (!namedTimeoutsStore) {
     return;
   }
   clearTimeout(namedTimeoutsStore.get(aId));
   namedTimeoutsStore.delete(aId);
 };
 /**
  * Same as `setNamedTimeout`, but invokes the callback only if the provided
  * predicate function returns true. Otherwise, the timeout is re-triggered.
  *
  * @param string aId
  *        A string identifier for the conditional timeout.
  * @param number aWait
  *        The amount of milliseconds to wait after no more events are fired.
  * @param function aPredicate
  *        The predicate function used to determine whether the timeout restarts.
  * @param function aCallback
  *        Invoked when no more events are fired after the specified time, and
  *        the provided predicate function returns true.
  */
 this.setConditionalTimeout = function setConditionalTimeout(aId, aWait, aPredicate, aCallback) {
   setNamedTimeout(aId, aWait, function maybeCallback() {
     if (aPredicate()) {
       aCallback();
       return;
     }
     setConditionalTimeout(aId, aWait, aPredicate, aCallback);
   });
 };
 /**
  * Clears a conditional timeout.
  * @see setConditionalTimeout
  *
  * @param string aId
  *        A string identifier for the conditional timeout.
  */
 this.clearConditionalTimeout = function clearConditionalTimeout(aId) {
   clearNamedTimeout(aId);
 };
 XPCOMUtils.defineLazyGetter(this, "namedTimeoutsStore", () => new Map());
 /**
  * Helpers for creating and messaging between UI components.
  */
 this.ViewHelpers = {
   /**
    * Convenience method, dispatching a custom event.
    *
    * @param nsIDOMNode aTarget
    *        A custom target element to dispatch the event from.
    * @param string aType
    *        The name of the event.
    * @param any aDetail
    *        The data passed when initializing the event.
    * @return boolean
    *         True if the event was cancelled or a registered handler
    *         called preventDefault.
    */
   dispatchEvent: function(aTarget, aType, aDetail) {
     if (!(aTarget instanceof Ci.nsIDOMNode)) {
       return true; // Event cancelled.
     }
     let document = aTarget.ownerDocument || aTarget;
     let dispatcher = aTarget.ownerDocument ? aTarget : document.documentElement;
     let event = document.createEvent("CustomEvent");
     event.initCustomEvent(aType, true, true, aDetail);
     return dispatcher.dispatchEvent(event);
   },
   /**
    * Helper delegating some of the DOM attribute methods of a node to a widget.
    *
    * @param object aWidget
    *        The widget to assign the methods to.
    * @param nsIDOMNode aNode
    *        A node to delegate the methods to.
    */
   delegateWidgetAttributeMethods: function(aWidget, aNode) {
     aWidget.getAttribute =
       aWidget.getAttribute || aNode.getAttribute.bind(aNode);
     aWidget.setAttribute =
       aWidget.setAttribute || aNode.setAttribute.bind(aNode);
     aWidget.removeAttribute =
       aWidget.removeAttribute || aNode.removeAttribute.bind(aNode);
   },
   /**
    * Helper delegating some of the DOM event methods of a node to a widget.
    *
    * @param object aWidget
    *        The widget to assign the methods to.
    * @param nsIDOMNode aNode
    *        A node to delegate the methods to.
    */
   delegateWidgetEventMethods: function(aWidget, aNode) {
     aWidget.addEventListener =
       aWidget.addEventListener || aNode.addEventListener.bind(aNode);
     aWidget.removeEventListener =
       aWidget.removeEventListener || aNode.removeEventListener.bind(aNode);
   },
   /**
    * Checks if the specified object looks like it's been decorated by an
    * event emitter.
    *
    * @return boolean
    *         True if it looks, walks and quacks like an event emitter.
    */
   isEventEmitter: function(aObject) {
     return aObject && aObject.on && aObject.off && aObject.once && aObject.emit;
   },
   /**
    * Checks if the specified object is an instance of a DOM node.
    *
    * @return boolean
    *         True if it's a node, false otherwise.
    */
   isNode: function(aObject) {
     return aObject instanceof Ci.nsIDOMNode ||
            aObject instanceof Ci.nsIDOMElement ||
            aObject instanceof Ci.nsIDOMDocumentFragment;
   },
   /**
    * Prevents event propagation when navigation keys are pressed.
    *
    * @param Event e
    *        The event to be prevented.
    */
   preventScrolling: function(e) {
     switch (e.keyCode) {
       case e.DOM_VK_UP:
       case e.DOM_VK_DOWN:
       case e.DOM_VK_LEFT:
       case e.DOM_VK_RIGHT:
       case e.DOM_VK_PAGE_UP:
       case e.DOM_VK_PAGE_DOWN:
       case e.DOM_VK_HOME:
       case e.DOM_VK_END:
         e.preventDefault();
         e.stopPropagation();
     }
   },
   /**
    * Sets a side pane hidden or visible.
    *
    * @param object aFlags
    *        An object containing some of the following properties:
    *        - visible: true if the pane should be shown, false to hide
    *        - animated: true to display an animation on toggle
    *        - delayed: true to wait a few cycles before toggle
    *        - callback: a function to invoke when the toggle finishes
    * @param nsIDOMNode aPane
    *        The element representing the pane to toggle.
    */
   togglePane: function(aFlags, aPane) {
     // Make sure a pane is actually available first.
     if (!aPane) {
       return;
     }
     // Hiding is always handled via margins, not the hidden attribute.
     aPane.removeAttribute("hidden");
     // Add a class to the pane to handle min-widths, margins and animations.
     if (!aPane.classList.contains("generic-toggled-side-pane")) {
       aPane.classList.add("generic-toggled-side-pane");
     }
     // Avoid useless toggles.
     if (aFlags.visible == !aPane.hasAttribute("pane-collapsed")) {
       if (aFlags.callback) aFlags.callback();
       return;
     }
     // The "animated" attributes enables animated toggles (slide in-out).
     if (aFlags.animated) {
       aPane.setAttribute("animated", "");
     } else {
       aPane.removeAttribute("animated");
     }
     // Computes and sets the pane margins in order to hide or show it.
     let doToggle = () => {
       if (aFlags.visible) {
         aPane.style.marginLeft = "0";
         aPane.style.marginRight = "0";
         aPane.removeAttribute("pane-collapsed");
       } else {
         let margin = ~~(aPane.getAttribute("width")) + 1;
         aPane.style.marginLeft = -margin + "px";
         aPane.style.marginRight = -margin + "px";
         aPane.setAttribute("pane-collapsed", "");
       }
       // Invoke the callback when the transition ended.
       if (aFlags.animated) {
         aPane.addEventListener("transitionend", function onEvent() {
           aPane.removeEventListener("transitionend", onEvent, false);
           if (aFlags.callback) aFlags.callback();
         }, false);
       }
       // Invoke the callback immediately since there's no transition.
       else {
         if (aFlags.callback) aFlags.callback();
       }
     }
     // Sometimes it's useful delaying the toggle a few ticks to ensure
     // a smoother slide in-out animation.
     if (aFlags.delayed) {
       aPane.ownerDocument.defaultView.setTimeout(doToggle, PANE_APPEARANCE_DELAY);
     } else {
       doToggle();
     }
   }
 };
 /**
  * Localization convenience methods.
  *
  * @param string aStringBundleName
  *        The desired string bundle's name.
  */
 ViewHelpers.L10N = function(aStringBundleName) {
   XPCOMUtils.defineLazyGetter(this, "stringBundle", () =>
     Services.strings.createBundle(aStringBundleName));
   XPCOMUtils.defineLazyGetter(this, "ellipsis", () =>
     Services.prefs.getComplexValue("intl.ellipsis", Ci.nsIPrefLocalizedString).data);
 };
 ViewHelpers.L10N.prototype = {
   stringBundle: null,
   /**
    * L10N shortcut function.
    *
    * @param string aName
    * @return string
    */
   getStr: function(aName) {
     return this.stringBundle.GetStringFromName(aName);
   },
   /**
    * L10N shortcut function.
    *
    * @param string aName
    * @param array aArgs
    * @return string
    */
   getFormatStr: function(aName, ...aArgs) {
     return this.stringBundle.formatStringFromName(aName, aArgs, aArgs.length);
   },
   /**
    * L10N shortcut function for numeric arguments that need to be formatted.
    * All numeric arguments will be fixed to 2 decimals and given a localized
    * decimal separator. Other arguments will be left alone.
    *
    * @param string aName
    * @param array aArgs
    * @return string
    */
   getFormatStrWithNumbers: function(aName, ...aArgs) {
     let newArgs = aArgs.map(x => typeof x == "number" ? this.numberWithDecimals(x, 2) : x);
     return this.stringBundle.formatStringFromName(aName, newArgs, newArgs.length);
   },
   /**
    * Converts a number to a locale-aware string format and keeps a certain
    * number of decimals.
    *
    * @param number aNumber
    *        The number to convert.
    * @param number aDecimals [optional]
    *        Total decimals to keep.
    * @return string
    *         The localized number as a string.
    */
   numberWithDecimals: function(aNumber, aDecimals = 0) {
     // If this is an integer, don't do anything special.
     if (aNumber == (aNumber | 0)) {
       return aNumber;
     }
     // Remove {n} trailing decimals. Can't use toFixed(n) because
     // toLocaleString converts the number to a string. Also can't use
     // toLocaleString(, { maximumFractionDigits: n }) because it's not
     // implemented on OS X (bug 368838). Gross.
     let localized = aNumber.toLocaleString(); // localize
     let padded = localized + new Array(aDecimals).join("0"); // pad with zeros
     let match = padded.match("([^]*?\\d{" + aDecimals + "})\\d*$");
     return match.pop();
   }
 };
 /**
  * Shortcuts for lazily accessing and setting various preferences.
  * Usage:
  *   let prefs = new ViewHelpers.Prefs("root.path.to.branch", {
  *     myIntPref: ["Int", "leaf.path.to.my-int-pref"],
  *     myCharPref: ["Char", "leaf.path.to.my-char-pref"],
  *     ...
  *   });
  *
  *   prefs.myCharPref = "foo";
  *   let aux = prefs.myCharPref;
  *
  * @param string aPrefsRoot
  *        The root path to the required preferences branch.
  * @param object aPrefsObject
  *        An object containing { accessorName: [prefType, prefName] } keys.
  */
 ViewHelpers.Prefs = function(aPrefsRoot = "", aPrefsObject = {}) {
   this.root = aPrefsRoot;
   for (let accessorName in aPrefsObject) {
     let [prefType, prefName] = aPrefsObject[accessorName];
     this.map(accessorName, prefType, prefName);
   }
 };
 ViewHelpers.Prefs.prototype = {
   /**
    * Helper method for getting a pref value.
    *
    * @param string aType
    * @param string aPrefName
    * @return any
    */
   _get: function(aType, aPrefName) {
     if (this[aPrefName] === undefined) {
       this[aPrefName] = Services.prefs["get" + aType + "Pref"](aPrefName);
     }
     return this[aPrefName];
   },
   /**
    * Helper method for setting a pref value.
    *
    * @param string aType
    * @param string aPrefName
    * @param any aValue
    */
   _set: function(aType, aPrefName, aValue) {
     Services.prefs["set" + aType + "Pref"](aPrefName, aValue);
     this[aPrefName] = aValue;
   },
   /**
    * Maps a property name to a pref, defining lazy getters and setters.
    * Supported types are "Bool", "Char", "Int" and "Json" (which is basically
    * just sugar for "Char" using the standard JSON serializer).
    *
    * @param string aAccessorName
    * @param string aType
    * @param string aPrefName
    * @param array aSerializer
    */
   map: function(aAccessorName, aType, aPrefName, aSerializer = { in: e => e, out: e => e }) {
     if (aType == "Json") {
       this.map(aAccessorName, "Char", aPrefName, { in: JSON.parse, out: JSON.stringify });
       return;
     }
     Object.defineProperty(this, aAccessorName, {
       get: () => aSerializer.in(this._get(aType, [this.root, aPrefName].join("."))),
       set: (e) => this._set(aType, [this.root, aPrefName].join("."), aSerializer.out(e))
     });
   }
 };
 /**
  * A generic Item is used to describe children present in a Widget.
  *
  * This is basically a very thin wrapper around an nsIDOMNode, with a few
  * characteristics, like a `value` and an `attachment`.
  *
  * The characteristics are optional, and their meaning is entirely up to you.
  * - The `value` should be a string, passed as an argument.
  * - The `attachment` is any kind of primitive or object, passed as an argument.
  *
  * Iterable via "for (let childItem of parentItem) { }".
  *
  * @param object aOwnerView
  *        The owner view creating this item.
  * @param nsIDOMNode aElement
  *        A prebuilt node to be wrapped.
  * @param string aValue
  *        A string identifying the node.
  * @param any aAttachment
  *        Some attached primitive/object.
  */
 function Item(aOwnerView, aElement, aValue, aAttachment) {
   this.ownerView = aOwnerView;
   this.attachment = aAttachment;
   this._value = aValue + "";
   this._prebuiltNode = aElement;
 };
 Item.prototype = {
   get value() { return this._value; },
   get target() { return this._target; },
   /**
    * Immediately appends a child item to this item.
    *
    * @param nsIDOMNode aElement
    *        An nsIDOMNode representing the child element to append.
    * @param object aOptions [optional]
    *        Additional options or flags supported by this operation:
    *          - attachment: some attached primitive/object for the item
    *          - attributes: a batch of attributes set to the displayed element
    *          - finalize: function invoked when the child item is removed
    * @return Item
    *         The item associated with the displayed element.
    */
   append: function(aElement, aOptions = {}) {
     let item = new Item(this, aElement, "", aOptions.attachment);
     // Entangle the item with the newly inserted child node.
     // Make sure this is done with the value returned by appendChild(),
     // to avoid storing a potential DocumentFragment.
     this._entangleItem(item, this._target.appendChild(aElement));
     // Handle any additional options after entangling the item.
     if (aOptions.attributes) {
       aOptions.attributes.forEach(e => item._target.setAttribute(e[0], e[1]));
     }
     if (aOptions.finalize) {
       item.finalize = aOptions.finalize;
     }
     // Return the item associated with the displayed element.
     return item;
   },
   /**
    * Immediately removes the specified child item from this item.
    *
    * @param Item aItem
    *        The item associated with the element to remove.
    */
   remove: function(aItem) {
     if (!aItem) {
       return;
     }
     this._target.removeChild(aItem._target);
     this._untangleItem(aItem);
   },
   /**
    * Entangles an item (model) with a displayed node element (view).
    *
    * @param Item aItem
    *        The item describing a target element.
    * @param nsIDOMNode aElement
    *        The element displaying the item.
    */
   _entangleItem: function(aItem, aElement) {
     this._itemsByElement.set(aElement, aItem);
     aItem._target = aElement;
   },
   /**
    * Untangles an item (model) from a displayed node element (view).
    *
    * @param Item aItem
    *        The item describing a target element.
    */
   _untangleItem: function(aItem) {
     if (aItem.finalize) {
       aItem.finalize(aItem);
     }
     for (let childItem of aItem) {
       aItem.remove(childItem);
     }
     this._unlinkItem(aItem);
     aItem._target = null;
   },
   /**
    * Deletes an item from the its parent's storage maps.
    *
    * @param Item aItem
    *        The item describing a target element.
    */
   _unlinkItem: function(aItem) {
     this._itemsByElement.delete(aItem._target);
   },
   /**
    * Returns a string representing the object.
    * @return string
    */
   toString: function() {
     return this._value + " :: " + this._target + " :: " + this.attachment;
   },
   _value: "",
   _target: null,
   _prebuiltNode: null,
   finalize: null,
   attachment: null
 };
 // Creating maps thousands of times for widgets with a large number of children
 // fills up a lot of memory. Make sure these are instantiated only if needed.
 DevToolsUtils.defineLazyPrototypeGetter(Item.prototype, "_itemsByElement", Map);
 /**
  * Some generic Widget methods handling Item instances.
  * Iterable via "for (let childItem of wrappedView) { }".
  *
  * Usage:
  *   function MyView() {
  *     this.widget = new MyWidget(document.querySelector(".my-node"));
  *   }
  *
  *   MyView.prototype = Heritage.extend(WidgetMethods, {
  *     myMethod: function() {},
  *     ...
  *   });
  *
  * See https://gist.github.com/victorporof/5749386 for more details.
  * The devtools/shared/widgets/SimpleListWidget.jsm is an implementation example.
  *
  * Language:
  *   - An "item" is an instance of an Item.
  *   - An "element" or "node" is a nsIDOMNode.
  *
  * The supplied widget can be any object implementing the following methods:
  *   - function:nsIDOMNode insertItemAt(aIndex:number, aNode:nsIDOMNode, aValue:string)
  *   - function:nsIDOMNode getItemAtIndex(aIndex:number)
  *   - function removeChild(aChild:nsIDOMNode)
  *   - function removeAllItems()
  *   - get:nsIDOMNode selectedItem()
  *   - set selectedItem(aChild:nsIDOMNode)
  *   - function getAttribute(aName:string)
  *   - function setAttribute(aName:string, aValue:string)
  *   - function removeAttribute(aName:string)
  *   - function addEventListener(aName:string, aCallback:function, aBubbleFlag:boolean)
  *   - function removeEventListener(aName:string, aCallback:function, aBubbleFlag:boolean)
  *
  * Optional methods that can be implemented by the widget:
  *   - function ensureElementIsVisible(aChild:nsIDOMNode)
  *
  * Optional attributes that may be handled (when calling get/set/removeAttribute):
  *   - "emptyText": label temporarily added when there are no items present
  *   - "headerText": label permanently added as a header
  *
  * For automagical keyboard and mouse accessibility, the widget should be an
  * event emitter with the following events:
  *   - "keyPress" -> (aName:string, aEvent:KeyboardEvent)
  *   - "mousePress" -> (aName:string, aEvent:MouseEvent)
  */
 this.WidgetMethods = {
   /**
    * Sets the element node or widget associated with this container.
    * @param nsIDOMNode | object aWidget
    */
   set widget(aWidget) {
     this._widget = aWidget;
     // Can't use a WeakMap for _itemsByValue because keys are strings, and
     // can't use one for _itemsByElement either, since it needs to be iterable.
     XPCOMUtils.defineLazyGetter(this, "_itemsByValue", () => new Map());
     XPCOMUtils.defineLazyGetter(this, "_itemsByElement", () => new Map());
     XPCOMUtils.defineLazyGetter(this, "_stagedItems", () => []);
     // Handle internal events emitted by the widget if necessary.
     if (ViewHelpers.isEventEmitter(aWidget)) {
       aWidget.on("keyPress", this._onWidgetKeyPress.bind(this));
       aWidget.on("mousePress", this._onWidgetMousePress.bind(this));
     }
   },
   /**
    * Gets the element node or widget associated with this container.
    * @return nsIDOMNode | object
    */
   get widget() this._widget,
   /**
    * Prepares an item to be added to this container. This allows, for example,
    * for a large number of items to be batched up before being sorted & added.
    *
    * If the "staged" flag is *not* set to true, the item will be immediately
    * inserted at the correct position in this container, so that all the items
    * still remain sorted. This can (possibly) be much slower than batching up
    * multiple items.
    *
    * By default, this container assumes that all the items should be displayed
    * sorted by their value. This can be overridden with the "index" flag,
    * specifying on which position should an item be appended. The "staged" and
    * "index" flags are mutually exclusive, meaning that all staged items
    * will always be appended.
    *
    * @param nsIDOMNode aElement
    *        A prebuilt node to be wrapped.
    * @param string aValue
    *        A string identifying the node.
    * @param object aOptions [optional]
    *        Additional options or flags supported by this operation:
    *          - attachment: some attached primitive/object for the item
    *          - staged: true to stage the item to be appended later
    *          - index: specifies on which position should the item be appended
    *          - attributes: a batch of attributes set to the displayed element
    *          - finalize: function invoked when the item is removed
    * @return Item
    *         The item associated with the displayed element if an unstaged push,
    *         undefined if the item was staged for a later commit.
    */
   push: function([aElement, aValue], aOptions = {}) {
     let item = new Item(this, aElement, aValue, aOptions.attachment);
     // Batch the item to be added later.
     if (aOptions.staged) {
       // An ulterior commit operation will ignore any specified index, so
       // no reason to keep it around.
       aOptions.index = undefined;
       return void this._stagedItems.push({ item: item, options: aOptions });
     }
     // Find the target position in this container and insert the item there.
     if (!("index" in aOptions)) {
       return this._insertItemAt(this._findExpectedIndexFor(item), item, aOptions);
     }
     // Insert the item at the specified index. If negative or out of bounds,
     // the item will be simply appended.
     return this._insertItemAt(aOptions.index, item, aOptions);
   },
   /**
    * Flushes all the prepared items into this container.
    * Any specified index on the items will be ignored. Everything is appended.
    *
    * @param object aOptions [optional]
    *        Additional options or flags supported by this operation:
    *          - sorted: true to sort all the items before adding them
    */
   commit: function(aOptions = {}) {
     let stagedItems = this._stagedItems;
     // Sort the items before adding them to this container, if preferred.
     if (aOptions.sorted) {
       stagedItems.sort((a, b) => this._currentSortPredicate(a.item, b.item));
     }
     // Append the prepared items to this container.
     for (let { item, options } of stagedItems) {
       this._insertItemAt(-1, item, options);
     }
     // Recreate the temporary items list for ulterior pushes.
     this._stagedItems.length = 0;
   },
   /**
    * Immediately removes the specified item from this container.
    *
    * @param Item aItem
    *        The item associated with the element to remove.
    */
   remove: function(aItem) {
     if (!aItem) {
       return;
     }
     this._widget.removeChild(aItem._target);
     this._untangleItem(aItem);
     if (!this._itemsByElement.size) {
       this._preferredValue = this.selectedValue;
       this._widget.selectedItem = null;
       this._widget.setAttribute("emptyText", this._emptyText);
     }
   },
   /**
    * Removes the item at the specified index from this container.
    *
    * @param number aIndex
    *        The index of the item to remove.
    */
   removeAt: function(aIndex) {
     this.remove(this.getItemAtIndex(aIndex));
   },
   /**
    * Removes all items from this container.
    */
   empty: function() {
     this._preferredValue = this.selectedValue;
     this._widget.selectedItem = null;
     this._widget.removeAllItems();
     this._widget.setAttribute("emptyText", this._emptyText);
     for (let [, item] of this._itemsByElement) {
       this._untangleItem(item);
     }
     this._itemsByValue.clear();
     this._itemsByElement.clear();
     this._stagedItems.length = 0;
   },
   /**
    * Ensures the specified item is visible in this container.
    *
    * @param Item aItem
    *        The item to bring into view.
    */
   ensureItemIsVisible: function(aItem) {
     this._widget.ensureElementIsVisible(aItem._target);
   },
   /**
    * Ensures the item at the specified index is visible in this container.
    *
    * @param number aIndex
    *        The index of the item to bring into view.
    */
   ensureIndexIsVisible: function(aIndex) {
     this.ensureItemIsVisible(this.getItemAtIndex(aIndex));
   },
   /**
    * Sugar for ensuring the selected item is visible in this container.
    */
   ensureSelectedItemIsVisible: function() {
     this.ensureItemIsVisible(this.selectedItem);
   },
   /**
    * If supported by the widget, the label string temporarily added to this
    * container when there are no child items present.
    */
   set emptyText(aValue) {
     this._emptyText = aValue;
     // Apply the emptyText attribute right now if there are no child items.
     if (!this._itemsByElement.size) {
       this._widget.setAttribute("emptyText", aValue);
     }
   },
   /**
    * If supported by the widget, the label string permanently added to this
    * container as a header.
    * @param string aValue
    */
   set headerText(aValue) {
     this._headerText = aValue;
     this._widget.setAttribute("headerText", aValue);
   },
   /**
    * Toggles all the items in this container hidden or visible.
    *
    * This does not change the default filtering predicate, so newly inserted
    * items will always be visible. Use WidgetMethods.filterContents if you care.
    *
    * @param boolean aVisibleFlag
    *        Specifies the intended visibility.
    */
   toggleContents: function(aVisibleFlag) {
     for (let [element, item] of this._itemsByElement) {
       element.hidden = !aVisibleFlag;
     }
   },
   /**
    * Toggles all items in this container hidden or visible based on a predicate.
    *
    * @param function aPredicate [optional]
    *        Items are toggled according to the return value of this function,
    *        which will become the new default filtering predicate in this container.
    *        If unspecified, all items will be toggled visible.
    */
   filterContents: function(aPredicate = this._currentFilterPredicate) {
     this._currentFilterPredicate = aPredicate;
     for (let [element, item] of this._itemsByElement) {
       element.hidden = !aPredicate(item);
     }
   },
   /**
    * Sorts all the items in this container based on a predicate.
    *
    * @param function aPredicate [optional]
    *        Items are sorted according to the return value of the function,
    *        which will become the new default sorting predicate in this container.
    *        If unspecified, all items will be sorted by their value.
    */
   sortContents: function(aPredicate = this._currentSortPredicate) {
     let sortedItems = this.items.sort(this._currentSortPredicate = aPredicate);
     for (let i = 0, len = sortedItems.length; i < len; i++) {
       this.swapItems(this.getItemAtIndex(i), sortedItems[i]);
     }
   },
   /**
    * Visually swaps two items in this container.
    *
    * @param Item aFirst
    *        The first item to be swapped.
    * @param Item aSecond
    *        The second item to be swapped.
    */
   swapItems: function(aFirst, aSecond) {
     if (aFirst == aSecond) { // We're just dandy, thank you.
       return;
     }
     let { _prebuiltNode: firstPrebuiltTarget, _target: firstTarget } = aFirst;
     let { _prebuiltNode: secondPrebuiltTarget, _target: secondTarget } = aSecond;
     // If the two items were constructed with prebuilt nodes as DocumentFragments,
     // then those DocumentFragments are now empty and need to be reassembled.
     if (firstPrebuiltTarget instanceof Ci.nsIDOMDocumentFragment) {
       for (let node of firstTarget.childNodes) {
         firstPrebuiltTarget.appendChild(node.cloneNode(true));
       }
     }
     if (secondPrebuiltTarget instanceof Ci.nsIDOMDocumentFragment) {
       for (let node of secondTarget.childNodes) {
         secondPrebuiltTarget.appendChild(node.cloneNode(true));
       }
     }
     // 1. Get the indices of the two items to swap.
     let i = this._indexOfElement(firstTarget);
     let j = this._indexOfElement(secondTarget);
     // 2. Remeber the selection index, to reselect an item, if necessary.
     let selectedTarget = this._widget.selectedItem;
     let selectedIndex = -1;
     if (selectedTarget == firstTarget) {
       selectedIndex = i;
     } else if (selectedTarget == secondTarget) {
       selectedIndex = j;
     }
     // 3. Silently nuke both items, nobody needs to know about this.
     this._widget.removeChild(firstTarget);
     this._widget.removeChild(secondTarget);
     this._unlinkItem(aFirst);
     this._unlinkItem(aSecond);
     // 4. Add the items again, but reversing their indices.
     this._insertItemAt.apply(this, i < j ? [i, aSecond] : [j, aFirst]);
     this._insertItemAt.apply(this, i < j ? [j, aFirst] : [i, aSecond]);
     // 5. Restore the previous selection, if necessary.
     if (selectedIndex == i) {
       this._widget.selectedItem = aFirst._target;
     } else if (selectedIndex == j) {
       this._widget.selectedItem = aSecond._target;
     }
     // 6. Let the outside world know that these two items were swapped.
     ViewHelpers.dispatchEvent(aFirst.target, "swap", [aSecond, aFirst]);
   },
   /**
    * Visually swaps two items in this container at specific indices.
    *
    * @param number aFirst
    *        The index of the first item to be swapped.
    * @param number aSecond
    *        The index of the second item to be swapped.
    */
   swapItemsAtIndices: function(aFirst, aSecond) {
     this.swapItems(this.getItemAtIndex(aFirst), this.getItemAtIndex(aSecond));
   },
   /**
    * Checks whether an item with the specified value is among the elements
    * shown in this container.
    *
    * @param string aValue
    *        The item's value.
    * @return boolean
    *         True if the value is known, false otherwise.
    */
   containsValue: function(aValue) {
     return this._itemsByValue.has(aValue) ||
            this._stagedItems.some(({ item }) => item._value == aValue);
   },
   /**
    * Gets the "preferred value". This is the latest selected item's value,
    * remembered just before emptying this container.
    * @return string
    */
   get preferredValue() {
     return this._preferredValue;
   },
   /**
    * Retrieves the item associated with the selected element.
    * @return Item | null
    */
   get selectedItem() {
     let selectedElement = this._widget.selectedItem;
     if (selectedElement) {
       return this._itemsByElement.get(selectedElement);
     }
     return null;
   },
   /**
    * Retrieves the selected element's index in this container.
    * @return number
    */
   get selectedIndex() {
     let selectedElement = this._widget.selectedItem;
     if (selectedElement) {
       return this._indexOfElement(selectedElement);
     }
     return -1;
   },
   /**
    * Retrieves the value of the selected element.
    * @return string
    */
   get selectedValue() {
     let selectedElement = this._widget.selectedItem;
     if (selectedElement) {
       return this._itemsByElement.get(selectedElement)._value;
     }
     return "";
   },
   /**
    * Retrieves the attachment of the selected element.
    * @return object | null
    */
   get selectedAttachment() {
     let selectedElement = this._widget.selectedItem;
     if (selectedElement) {
       return this._itemsByElement.get(selectedElement).attachment;
     }
     return null;
   },
   /**
    * Selects the element with the entangled item in this container.
    * @param Item | function aItem
    */
   set selectedItem(aItem) {
     // A predicate is allowed to select a specific item.
     // If no item is matched, then the current selection is removed.
     if (typeof aItem == "function") {
       aItem = this.getItemForPredicate(aItem);
     }
     // A falsy item is allowed to invalidate the current selection.
     let targetElement = aItem ? aItem._target : null;
     let prevElement = this._widget.selectedItem;
     // Make sure the selected item's target element is focused and visible.
     if (this.autoFocusOnSelection && targetElement) {
       targetElement.focus();
     }
     if (this.maintainSelectionVisible && targetElement) {
       if ("ensureElementIsVisible" in this._widget) {
         this._widget.ensureElementIsVisible(targetElement);
       }
     }
     // Prevent selecting the same item again and avoid dispatching
     // a redundant selection event, so return early.
     if (targetElement != prevElement) {
       this._widget.selectedItem = targetElement;
       let dispTarget = targetElement || prevElement;
       let dispName = this.suppressSelectionEvents ? "suppressed-select" : "select";
       ViewHelpers.dispatchEvent(dispTarget, dispName, aItem);
     }
   },
   /**
    * Selects the element at the specified index in this container.
    * @param number aIndex
    */
   set selectedIndex(aIndex) {
     let targetElement = this._widget.getItemAtIndex(aIndex);
     if (targetElement) {
       this.selectedItem = this._itemsByElement.get(targetElement);
       return;
     }
     this.selectedItem = null;
   },
   /**
    * Selects the element with the specified value in this container.
    * @param string aValue
    */
   set selectedValue(aValue) {
     this.selectedItem = this._itemsByValue.get(aValue);
   },
   /**
    * Specifies if this container should try to keep the selected item visible.
    * (For example, when new items are added the selection is brought into view).
    */
   maintainSelectionVisible: true,
   /**
    * Specifies if "select" events dispatched from the elements in this container
    * when their respective items are selected should be suppressed or not.
    *
    * If this flag is set to true, then consumers of this container won't
    * be normally notified when items are selected.
    */
   suppressSelectionEvents: false,
   /**
    * Focus this container the first time an element is inserted?
    *
    * If this flag is set to true, then when the first item is inserted in
    * this container (and thus it's the only item available), its corresponding
    * target element is focused as well.
    */
   autoFocusOnFirstItem: true,
   /**
    * Focus on selection?
    *
    * If this flag is set to true, then whenever an item is selected in
    * this container (e.g. via the selectedIndex or selectedItem setters),
    * its corresponding target element is focused as well.
    *
    * You can disable this flag, for example, to maintain a certain node
    * focused but visually indicate a different selection in this container.
    */
   autoFocusOnSelection: true,
   /**
    * Focus on input (e.g. mouse click)?
    *
    * If this flag is set to true, then whenever an item receives user input in
    * this container, its corresponding target element is focused as well.
    */
   autoFocusOnInput: true,
   /**
    * When focusing on input, allow right clicks?
    * @see WidgetMethods.autoFocusOnInput
    */
   allowFocusOnRightClick: false,
   /**
    * The number of elements in this container to jump when Page Up or Page Down
    * keys are pressed. If falsy, then the page size will be based on the
    * number of visible items in the container.
    */
   pageSize: 0,
   /**
    * Focuses the first visible item in this container.
    */
   focusFirstVisibleItem: function() {
     this.focusItemAtDelta(-this.itemCount);
   },
   /**
    * Focuses the last visible item in this container.
    */
   focusLastVisibleItem: function() {
     this.focusItemAtDelta(+this.itemCount);
   },
   /**
    * Focuses the next item in this container.
    */
   focusNextItem: function() {
     this.focusItemAtDelta(+1);
   },
   /**
    * Focuses the previous item in this container.
    */
   focusPrevItem: function() {
     this.focusItemAtDelta(-1);
   },
   /**
    * Focuses another item in this container based on the index distance
    * from the currently focused item.
    *
    * @param number aDelta
    *        A scalar specifying by how many items should the selection change.
    */
   focusItemAtDelta: function(aDelta) {
     // Make sure the currently selected item is also focused, so that the
     // command dispatcher mechanism has a relative node to work with.
     // If there's no selection, just select an item at a corresponding index
     // (e.g. the first item in this container if aDelta <= 1).
     let selectedElement = this._widget.selectedItem;
     if (selectedElement) {
       selectedElement.focus();
     } else {
       this.selectedIndex = Math.max(0, aDelta - 1);
       return;
     }
     let direction = aDelta > 0 ? "advanceFocus" : "rewindFocus";
     let distance = Math.abs(Math[aDelta > 0 ? "ceil" : "floor"](aDelta));
     while (distance--) {
       if (!this._focusChange(direction)) {
         break; // Out of bounds.
       }
     }
     // Synchronize the selected item as being the currently focused element.
     this.selectedItem = this.getItemForElement(this._focusedElement);
   },
   /**
    * Focuses the next or previous item in this container.
    *
    * @param string aDirection
    *        Either "advanceFocus" or "rewindFocus".
    * @return boolean
    *         False if the focus went out of bounds and the first or last item
    *         in this container was focused instead.
    */
   _focusChange: function(aDirection) {
     let commandDispatcher = this._commandDispatcher;
     let prevFocusedElement = commandDispatcher.focusedElement;
     let currFocusedElement;
     do {
       commandDispatcher.suppressFocusScroll = true;
       commandDispatcher[aDirection]();
       currFocusedElement = commandDispatcher.focusedElement;
       // Make sure the newly focused item is a part of this container. If the
       // focus goes out of bounds, revert the previously focused item.
       if (!this.getItemForElement(currFocusedElement)) {
         prevFocusedElement.focus();
         return false;
       }
     } while (!WIDGET_FOCUSABLE_NODES.has(currFocusedElement.tagName));
     // Focus remained within bounds.
     return true;
   },
   /**
    * Gets the command dispatcher instance associated with this container's DOM.
    * If there are no items displayed in this container, null is returned.
    * @return nsIDOMXULCommandDispatcher | null
    */
   get _commandDispatcher() {
     if (this._cachedCommandDispatcher) {
       return this._cachedCommandDispatcher;
     }
     let someElement = this._widget.getItemAtIndex(0);
     if (someElement) {
       let commandDispatcher = someElement.ownerDocument.commandDispatcher;
       return this._cachedCommandDispatcher = commandDispatcher;
     }
     return null;
   },
   /**
    * Gets the currently focused element in this container.
    *
    * @return nsIDOMNode
    *         The focused element, or null if nothing is found.
    */
   get _focusedElement() {
     let commandDispatcher = this._commandDispatcher;
     if (commandDispatcher) {
       return commandDispatcher.focusedElement;
     }
     return null;
   },
   /**
    * Gets the item in the container having the specified index.
    *
    * @param number aIndex
    *        The index used to identify the element.
    * @return Item
    *         The matched item, or null if nothing is found.
    */
   getItemAtIndex: function(aIndex) {
     return this.getItemForElement(this._widget.getItemAtIndex(aIndex));
   },
   /**
    * Gets the item in the container having the specified value.
    *
    * @param string aValue
    *        The value used to identify the element.
    * @return Item
    *         The matched item, or null if nothing is found.
    */
   getItemByValue: function(aValue) {
     return this._itemsByValue.get(aValue);
   },
   /**
    * Gets the item in the container associated with the specified element.
    *
    * @param nsIDOMNode aElement
    *        The element used to identify the item.
    * @param object aFlags [optional]
    *        Additional options for showing the source. Supported options:
    *          - noSiblings: if siblings shouldn't be taken into consideration
    *                        when searching for the associated item.
    * @return Item
    *         The matched item, or null if nothing is found.
    */
   getItemForElement: function(aElement, aFlags = {}) {
     while (aElement) {
       let item = this._itemsByElement.get(aElement);
       // Also search the siblings if allowed.
       if (!aFlags.noSiblings) {
         item = item ||
           this._itemsByElement.get(aElement.nextElementSibling) ||
           this._itemsByElement.get(aElement.previousElementSibling);
       }
       if (item) {
         return item;
       }
       aElement = aElement.parentNode;
     }
     return null;
   },
   /**
    * Gets a visible item in this container validating a specified predicate.
    *
    * @param function aPredicate
    *        The first item which validates this predicate is returned
    * @return Item
    *         The matched item, or null if nothing is found.
    */
   getItemForPredicate: function(aPredicate, aOwner = this) {
     // Recursively check the items in this widget for a predicate match.
     for (let [element, item] of aOwner._itemsByElement) {
       let match;
       if (aPredicate(item) && !element.hidden) {
         match = item;
       } else {
         match = this.getItemForPredicate(aPredicate, item);
       }
       if (match) {
         return match;
       }
     }
     // Also check the staged items. No need to do this recursively since
     // they're not even appended to the view yet.
     for (let { item } of this._stagedItems) {
       if (aPredicate(item)) {
         return item;
       }
     }
     return null;
   },
   /**
    * Shortcut function for getItemForPredicate which works on item attachments.
    * @see getItemForPredicate
    */
   getItemForAttachment: function(aPredicate, aOwner = this) {
     return this.getItemForPredicate(e => aPredicate(e.attachment));
   },
   /**
    * Finds the index of an item in the container.
    *
    * @param Item aItem
    *        The item get the index for.
    * @return number
    *         The index of the matched item, or -1 if nothing is found.
    */
   indexOfItem: function(aItem) {
     return this._indexOfElement(aItem._target);
   },
   /**
    * Finds the index of an element in the container.
    *
    * @param nsIDOMNode aElement
    *        The element get the index for.
    * @return number
    *         The index of the matched element, or -1 if nothing is found.
    */
   _indexOfElement: function(aElement) {
     for (let i = 0; i < this._itemsByElement.size; i++) {
       if (this._widget.getItemAtIndex(i) == aElement) {
         return i;
       }
     }
     return -1;
   },
   /**
    * Gets the total number of items in this container.
    * @return number
    */
   get itemCount() {
     return this._itemsByElement.size;
   },
   /**
    * Returns a list of items in this container, in the displayed order.
    * @return array
    */
   get items() {
     let store = [];
     let itemCount = this.itemCount;
     for (let i = 0; i < itemCount; i++) {
       store.push(this.getItemAtIndex(i));
     }
     return store;
   },
   /**
    * Returns a list of values in this container, in the displayed order.
    * @return array
    */
   get values() {
     return this.items.map(e => e._value);
   },
   /**
    * Returns a list of attachments in this container, in the displayed order.
    * @return array
    */
   get attachments() {
     return this.items.map(e => e.attachment);
   },
   /**
    * Returns a list of all the visible (non-hidden) items in this container,
    * in the displayed order
    * @return array
    */
   get visibleItems() {
     return this.items.filter(e => !e._target.hidden);
   },
   /**
    * Checks if an item is unique in this container. If an item's value is an
    * empty string, "undefined" or "null", it is considered unique.
    *
    * @param Item aItem
    *        The item for which to verify uniqueness.
    * @return boolean
    *         True if the item is unique, false otherwise.
    */
   isUnique: function(aItem) {
     let value = aItem._value;
     if (value == "" || value == "undefined" || value == "null") {
       return true;
     }
     return !this._itemsByValue.has(value);
   },
   /**
    * Checks if an item is eligible for this container. By default, this checks
    * whether an item is unique and has a prebuilt target node.
    *
    * @param Item aItem
    *        The item for which to verify eligibility.
    * @return boolean
    *         True if the item is eligible, false otherwise.
    */
   isEligible: function(aItem) {
     return this.isUnique(aItem) && aItem._prebuiltNode;
   },
   /**
    * Finds the expected item index in this container based on the default
    * sort predicate.
    *
    * @param Item aItem
    *        The item for which to get the expected index.
    * @return number
    *         The expected item index.
    */
   _findExpectedIndexFor: function(aItem) {
     let itemCount = this.itemCount;
     for (let i = 0; i < itemCount; i++) {
       if (this._currentSortPredicate(this.getItemAtIndex(i), aItem) > 0) {
         return i;
       }
     }
     return itemCount;
   },
   /**
    * Immediately inserts an item in this container at the specified index.
    *
    * @param number aIndex
    *        The position in the container intended for this item.
    * @param Item aItem
    *        The item describing a target element.
    * @param object aOptions [optional]
    *        Additional options or flags supported by this operation:
    *          - attributes: a batch of attributes set to the displayed element
    *          - finalize: function when the item is untangled (removed)
    * @return Item
    *         The item associated with the displayed element, null if rejected.
    */
   _insertItemAt: function(aIndex, aItem, aOptions = {}) {
     if (!this.isEligible(aItem)) {
       return null;
     }
     // Entangle the item with the newly inserted node.
     // Make sure this is done with the value returned by insertItemAt(),
     // to avoid storing a potential DocumentFragment.
     let node = aItem._prebuiltNode;
     let attachment = aItem.attachment;
     this._entangleItem(aItem, this._widget.insertItemAt(aIndex, node, attachment));
     // Handle any additional options after entangling the item.
     if (!this._currentFilterPredicate(aItem)) {
       aItem._target.hidden = true;
     }
     if (this.autoFocusOnFirstItem && this._itemsByElement.size == 1) {
       aItem._target.focus();
     }
     if (aOptions.attributes) {
       aOptions.attributes.forEach(e => aItem._target.setAttribute(e[0], e[1]));
     }
     if (aOptions.finalize) {
       aItem.finalize = aOptions.finalize;
     }
     // Hide the empty text if the selection wasn't lost.
     this._widget.removeAttribute("emptyText");
     // Return the item associated with the displayed element.
     return aItem;
   },
   /**
    * Entangles an item (model) with a displayed node element (view).
    *
    * @param Item aItem
    *        The item describing a target element.
    * @param nsIDOMNode aElement
    *        The element displaying the item.
    */
   _entangleItem: function(aItem, aElement) {
     this._itemsByValue.set(aItem._value, aItem);
     this._itemsByElement.set(aElement, aItem);
     aItem._target = aElement;
   },
   /**
    * Untangles an item (model) from a displayed node element (view).
    *
    * @param Item aItem
    *        The item describing a target element.
    */
   _untangleItem: function(aItem) {
     if (aItem.finalize) {
       aItem.finalize(aItem);
     }
     for (let childItem of aItem) {
       aItem.remove(childItem);
     }
     this._unlinkItem(aItem);
     aItem._target = null;
   },
   /**
    * Deletes an item from the its parent's storage maps.
    *
    * @param Item aItem
    *        The item describing a target element.
    */
   _unlinkItem: function(aItem) {
     this._itemsByValue.delete(aItem._value);
     this._itemsByElement.delete(aItem._target);
   },
   /**
    * The keyPress event listener for this container.
    * @param string aName
    * @param KeyboardEvent aEvent
    */
   _onWidgetKeyPress: function(aName, aEvent) {
     // Prevent scrolling when pressing navigation keys.
     ViewHelpers.preventScrolling(aEvent);
     switch (aEvent.keyCode) {
       case aEvent.DOM_VK_UP:
       case aEvent.DOM_VK_LEFT:
         this.focusPrevItem();
         return;
       case aEvent.DOM_VK_DOWN:
       case aEvent.DOM_VK_RIGHT:
         this.focusNextItem();
         return;
       case aEvent.DOM_VK_PAGE_UP:
         this.focusItemAtDelta(-(this.pageSize || (this.itemCount / PAGE_SIZE_ITEM_COUNT_RATIO)));
         return;
       case aEvent.DOM_VK_PAGE_DOWN:
         this.focusItemAtDelta(+(this.pageSize || (this.itemCount / PAGE_SIZE_ITEM_COUNT_RATIO)));
         return;
       case aEvent.DOM_VK_HOME:
         this.focusFirstVisibleItem();
         return;
       case aEvent.DOM_VK_END:
         this.focusLastVisibleItem();
         return;
     }
   },
   /**
    * The mousePress event listener for this container.
    * @param string aName
    * @param MouseEvent aEvent
    */
   _onWidgetMousePress: function(aName, aEvent) {
     if (aEvent.button != 0 && !this.allowFocusOnRightClick) {
       // Only allow left-click to trigger this event.
       return;
     }
     let item = this.getItemForElement(aEvent.target);
     if (item) {
       // The container is not empty and we clicked on an actual item.
       this.selectedItem = item;
       // Make sure the current event's target element is also focused.
       this.autoFocusOnInput && item._target.focus();
     }
   },
   /**
    * The predicate used when filtering items. By default, all items in this
    * view are visible.
    *
    * @param Item aItem
    *        The item passing through the filter.
    * @return boolean
    *         True if the item should be visible, false otherwise.
    */
   _currentFilterPredicate: function(aItem) {
     return true;
   },
   /**
    * The predicate used when sorting items. By default, items in this view
    * are sorted by their label.
    *
    * @param Item aFirst
    *        The first item used in the comparison.
    * @param Item aSecond
    *        The second item used in the comparison.
    * @return number
    *         -1 to sort aFirst to a lower index than aSecond
    *          0 to leave aFirst and aSecond unchanged with respect to each other
    *          1 to sort aSecond to a lower index than aFirst
    */
   _currentSortPredicate: function(aFirst, aSecond) {
     return +(aFirst._value.toLowerCase() > aSecond._value.toLowerCase());
   },
   /**
    * Call a method on this widget named `aMethodName`. Any further arguments are
    * passed on to the method. Returns the result of the method call.
    *
    * @param String aMethodName
    *        The name of the method you want to call.
    * @param aArgs
    *        Optional. Any arguments you want to pass through to the method.
    */
   callMethod: function(aMethodName, ...aArgs) {
     return this._widget[aMethodName].apply(this._widget, aArgs);
   },
   _widget: null,
   _emptyText: "",
   _headerText: "",
   _preferredValue: "",
   _cachedCommandDispatcher: null
 };
 /**
  * A generator-iterator over all the items in this container.
  */
 Item.prototype["@@iterator"] =
 WidgetMethods["@@iterator"] = function*() {
   yield* this._itemsByElement.values();
 };

The Tor Browser / annotate

browser/devtools/shared/widgets/ViewHelpers.jsm@6474c204b198 (annotated)

browser/devtools/shared/widgets/ViewHelpers.jsm