The Tor Browser: browser/components/customizableui/src/ScrollbarSampler.jsm@ca08bd8f51b2

     1 /* This Source Code Form is subject to the terms of the Mozilla Public

     2  * License, v. 2.0. If a copy of the MPL was not distributed with this

     3  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

     5 "use strict";

     7 this.EXPORTED_SYMBOLS = ["ScrollbarSampler"];

     9 const {classes: Cc, interfaces: Ci, utils: Cu, results: Cr} = Components;

    11 Cu.import("resource://gre/modules/Services.jsm");

    12 Cu.import("resource://gre/modules/XPCOMUtils.jsm");

    13 XPCOMUtils.defineLazyModuleGetter(this, "Promise",

    14                                   "resource://gre/modules/Promise.jsm");

    16 let gSystemScrollbarWidth = null;

    18 this.ScrollbarSampler = {

    19   getSystemScrollbarWidth: function() {

    20     let deferred = Promise.defer();

    22     if (gSystemScrollbarWidth !== null) {

    23       deferred.resolve(gSystemScrollbarWidth);

    24       return deferred.promise;

    25     }

    27     this._sampleSystemScrollbarWidth().then(function(systemScrollbarWidth) {

    28       gSystemScrollbarWidth = systemScrollbarWidth;

    29       deferred.resolve(gSystemScrollbarWidth);

    30     });

    31     return deferred.promise;

    32   },

    34   resetSystemScrollbarWidth: function() {

    35     gSystemScrollbarWidth = null;

    36   },

    38   _sampleSystemScrollbarWidth: function() {

    39     let deferred = Promise.defer();

    40     let hwin = Services.appShell.hiddenDOMWindow;

    41     let hdoc = hwin.document.documentElement;

    42     let iframe = hwin.document.createElementNS("http://www.w3.org/1999/xhtml",

    43                                                "html:iframe");

    44     iframe.setAttribute("srcdoc", '<body style="overflow-y: scroll"></body>');

    45     hdoc.appendChild(iframe);

    47     let cwindow = iframe.contentWindow;

    48     let utils = cwindow.QueryInterface(Ci.nsIInterfaceRequestor)

    49                        .getInterface(Ci.nsIDOMWindowUtils);

    51     cwindow.addEventListener("load", function onLoad(aEvent) {

    52       cwindow.removeEventListener("load", onLoad);

    53       let sbWidth = {};

    54       try {

    55         utils.getScrollbarSize(true, sbWidth, {});

    56       } catch(e) {

    57         Cu.reportError("Could not sample scrollbar size: " + e + " -- " +

    58                        e.stack);

    59         sbWidth.value = 0;

    60       }

    61       // Minimum width of 10 so that we have enough padding:

    62       sbWidth.value = Math.max(sbWidth.value, 10);

    63       deferred.resolve(sbWidth.value);

    64       iframe.remove();

    65     });

    67     return deferred.promise;

    68   }

    69 };

    70 Object.freeze(this.ScrollbarSampler);

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