6e1e69bcce
Whenever endpoint-provided value changes, update corresponding attribute on the plugin provided element. With this change, plugins can receive updates to the parameters if that's needed. To take advantage of this change, plugin has few options: - use a Polymer observers or computed properties - use `plugin.attributeHelper(element).bind(propertyName, callback)` Bug: Issue 8162 Change-Id: Ie95f30dd8d840be62cb3370bf39de96672638fd7
100 lines
3.0 KiB
JavaScript
100 lines
3.0 KiB
JavaScript
// Copyright (C) 2017 The Android Open Source Project
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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(function(window) {
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'use strict';
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function GrAttributeHelper(element) {
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this.element = element;
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this._promises = {};
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}
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GrAttributeHelper.prototype._getChangedEventName = function(name) {
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return name.replace(/([a-z])([A-Z])/g, '$1-$2').toLowerCase() + '-changed';
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};
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/**
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* Returns true if the property is defined on wrapped element.
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* @param {string} name
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* @return {boolean}
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*/
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GrAttributeHelper.prototype._elementHasProperty = function(name) {
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return this.element[name] !== undefined;
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};
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GrAttributeHelper.prototype._reportValue = function(callback, value) {
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try {
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callback(value);
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} catch (e) {
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console.info(e);
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}
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};
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/**
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* Binds callback to property updates.
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*
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* @param {string} name Property name.
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* @param {function(?)} callback
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* @return {function()} Unbind function.
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*/
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GrAttributeHelper.prototype.bind = function(name, callback) {
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const attributeChangedEventName = this._getChangedEventName(name);
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const changedHandler = e => this._reportValue(callback, e.detail.value);
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const unbind = () => this.element.removeEventListener(
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attributeChangedEventName, changedHandler);
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this.element.addEventListener(
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attributeChangedEventName, changedHandler);
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if (this._elementHasProperty(name)) {
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this._reportValue(callback, this.element[name]);
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}
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return unbind;
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};
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/**
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* Get value of the property from wrapped object. Waits for the property
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* to be initialized if it isn't defined.
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*
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* @param {string} name Property name.
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* @return {!Promise<?>}
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*/
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GrAttributeHelper.prototype.get = function(name) {
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if (this._elementHasProperty(name)) {
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return Promise.resolve(this.element[name]);
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}
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if (!this._promises[name]) {
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let resolve;
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const promise = new Promise(r => resolve = r);
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const unbind = this.bind(name, value => {
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resolve(value);
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unbind();
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});
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this._promises[name] = promise;
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}
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return this._promises[name];
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};
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/**
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* Sets value and dispatches event to force notify.
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*
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* @param {string} name Property name.
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* @param {?} value
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*/
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GrAttributeHelper.prototype.set = function(name, value) {
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this.element[name] = value;
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this.element.dispatchEvent(
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new CustomEvent(this._getChangedEventName(name), {detail: {value}}));
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};
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window.GrAttributeHelper = GrAttributeHelper;
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})(window);
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