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resize-observer-stub.js
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resize-observer-stub.js
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/**
* Copyright 2020 The AMP HTML Authors. All Rights Reserved.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS-IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
/**
* @fileoverview
* See https://developer.mozilla.org/en-US/docs/Web/API/ResizeObserver
*
* This is the stub to support ResizeObserver. It's installed from
* polyfills/resize-observer.js and upgraded from the
* amp-resize-observer-polyfill extension.
*/
const UPGRADERS = '_upgraders';
const STUB = '_stub';
/**
* @param {!Window} win
* @return {boolean}
* @visibleForTesting
*/
export function shouldLoadPolyfill(win) {
return !win.ResizeObserver || !!win.ResizeObserver[STUB];
}
/**
* Installs the ResOb stubs.
*
* @param {!Window} win
*/
export function installStub(win) {
if (win.ResizeObserver) {
return;
}
win.ResizeObserver = ResizeObserverStub;
win.ResizeObserver[STUB] = ResizeObserverStub;
}
/**
* @param {!Window} win
* @param {function()} installer
*/
export function upgradePolyfill(win, installer) {
// Can't use the ResizeObserverStub here directly since it's a separate
// instance deployed in v0.js vs the polyfill extension.
const Stub = /** @type {typeof ResizeObserverStub} */ (win.ResizeObserver[
STUB
]);
if (Stub) {
delete win.ResizeObserver;
delete win.ResizeObserverEntry;
installer();
const Polyfill = win.ResizeObserver;
const upgraders = Stub[UPGRADERS].slice(0);
const microtask = Promise.resolve();
const upgrade = (upgrader) => {
microtask.then(() => upgrader(Polyfill));
};
if (upgraders.length > 0) {
/** @type {!Array} */ (upgraders).forEach(upgrade);
}
Stub[UPGRADERS] = /** @type {!Array<function(typeof ResizeObserver)>} */ ({
'push': upgrade,
});
} else {
// Even if this is not the stub, we still may need to install the polyfill.
// See `shouldLoadPolyfill` for more info.
installer();
}
}
/**
* The stub for `ResizeObserver`. Implements the same interface, but
* keeps the tracked elements in memory until the actual polyfill arives.
* This stub is necessary because the polyfill itself is significantly bigger.
*/
export class ResizeObserverStub {
/**
* @param {!ResizeObserverCallback} callback
*/
constructor(callback) {
/** @private @const */
this.callback_ = callback;
/** @private {?Array<!Element>} */
this.elements_ = [];
/** @private {?ResizeObserver} */
this.inst_ = null;
// Wait for the upgrade.
ResizeObserverStub[UPGRADERS].push(this.upgrade_.bind(this));
}
/**
* @return {*}
*/
disconnect() {
if (this.inst_) {
this.inst_.disconnect();
} else {
this.elements_.length = 0;
}
}
/**
* @param {!Element} target
*/
observe(target) {
if (this.inst_) {
this.inst_.observe(target);
} else {
if (this.elements_.indexOf(target) == -1) {
this.elements_.push(target);
}
}
}
/**
* @param {!Element} target
*/
unobserve(target) {
if (this.inst_) {
this.inst_.unobserve(target);
} else {
const index = this.elements_.indexOf(target);
if (index != -1) {
this.elements_.splice(index, 1);
}
}
}
/**
* @param {typeof ResizeObserver} constr
* @private
*/
upgrade_(constr) {
const inst = new constr(this.callback_, this.options_);
this.inst_ = inst;
this.elements_.forEach((e) => inst.observe(e));
this.elements_ = null;
}
}
/**
* @type {!Array<function(typeof ResizeObserver)>}
*/
ResizeObserverStub[UPGRADERS] = [];
/** @visibleForTesting */
export function resetStubsForTesting() {
ResizeObserverStub[UPGRADERS] = [];
}