The Tor Browser: toolkit/modules/sessionstore/ScrollPosition.jsm@b8a032363ba2

Incorporate requested changes from Mozilla in review:
https://bugzilla.mozilla.org/show_bug.cgi?id=1123480#c6

     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 file,

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

     5 "use strict";

     7 this.EXPORTED_SYMBOLS = ["ScrollPosition"];

     9 const Ci = Components.interfaces;

    11 /**

    12  * It provides methods to collect and restore scroll positions for single

    13  * frames and frame trees.

    14  *

    15  * This is a child process module.

    16  */

    17 this.ScrollPosition = Object.freeze({

    18   /**

    19    * Collects scroll position data for any given |frame| in the frame hierarchy.

    20    *

    21    * @param frame (DOMWindow)

    22    *

    23    * @return {scroll: "x,y"} e.g. {scroll: "100,200"}

    24    *         Returns null when there is no scroll data we want to store for the

    25    *         given |frame|.

    26    */

    27   collect: function (frame) {

    28     let ifreq = frame.QueryInterface(Ci.nsIInterfaceRequestor);

    29     let utils = ifreq.getInterface(Ci.nsIDOMWindowUtils);

    30     let scrollX = {}, scrollY = {};

    31     utils.getScrollXY(false /* no layout flush */, scrollX, scrollY);

    33     if (scrollX.value || scrollY.value) {

    34       return {scroll: scrollX.value + "," + scrollY.value};

    35     }

    37     return null;

    38   },

    40   /**

    41    * Restores scroll position data for any given |frame| in the frame hierarchy.

    42    *

    43    * @param frame (DOMWindow)

    44    * @param value (object, see collect())

    45    */

    46   restore: function (frame, value) {

    47     let match;

    49     if (value && (match = /(\d+),(\d+)/.exec(value))) {

    50       frame.scrollTo(match[1], match[2]);

    51     }

    52   },

    54   /**

    55    * Restores scroll position data for the current frame hierarchy starting at

    56    * |root| using the given scroll position |data|.

    57    *

    58    * If the given |root| frame's hierarchy doesn't match that of the given

    59    * |data| object we will silently discard data for unreachable frames. We

    60    * may as well assign scroll positions to the wrong frames if some were

    61    * reordered or removed.

    62    *

    63    * @param root (DOMWindow)

    64    * @param data (object)

    65    *        {

    66    *          scroll: "100,200",

    67    *          children: [

    68    *            {scroll: "100,200"},

    69    *            null,

    70    *            {scroll: "200,300", children: [ ... ]}

    71    *          ]

    72    *        }

    73    */

    74   restoreTree: function (root, data) {

    75     if (data.hasOwnProperty("scroll")) {

    76       this.restore(root, data.scroll);

    77     }

    79     if (!data.hasOwnProperty("children")) {

    80       return;

    81     }

    83     let frames = root.frames;

    84     data.children.forEach((child, index) => {

    85       if (child && index < frames.length) {

    86         this.restoreTree(frames[index], child);

    87       }

    88     });

    89   }

    90 });

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