polygerrit-ui/app/elements/plugins/gr-attribute-helper/gr-attribute-helper.js

/**
 * @license
 * Copyright (C) 2017 The Android Open Source Project
 *
 * 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.
 */

/** @constructor */
export function GrAttributeHelper(element) {
  this.element = element;
  this._promises = {};
}

GrAttributeHelper.prototype._getChangedEventName = function(name) {
  return name.replace(/([a-z])([A-Z])/g, '$1-$2').toLowerCase() + '-changed';
};

/**
 * Returns true if the property is defined on wrapped element.
 *
 * @param {string} name
 * @return {boolean}
 */
GrAttributeHelper.prototype._elementHasProperty = function(name) {
  return this.element[name] !== undefined;
};

GrAttributeHelper.prototype._reportValue = function(callback, value) {
  try {
    callback(value);
  } catch (e) {
    console.info(e);
  }
};

/**
 * Binds callback to property updates.
 *
 * @param {string} name Property name.
 * @param {function(?)} callback
 * @return {function()} Unbind function.
 */
GrAttributeHelper.prototype.bind = function(name, callback) {
  const attributeChangedEventName = this._getChangedEventName(name);
  const changedHandler = e => this._reportValue(callback, e.detail.value);
  const unbind = () => this.element.removeEventListener(
      attributeChangedEventName, changedHandler);
  this.element.addEventListener(
      attributeChangedEventName, changedHandler);
  if (this._elementHasProperty(name)) {
    this._reportValue(callback, this.element[name]);
  }
  return unbind;
};

/**
 * Get value of the property from wrapped object. Waits for the property
 * to be initialized if it isn't defined.
 *
 * @param {string} name Property name.
 * @return {!Promise<?>}
 */
GrAttributeHelper.prototype.get = function(name) {
  if (this._elementHasProperty(name)) {
    return Promise.resolve(this.element[name]);
  }
  if (!this._promises[name]) {
    let resolve;
    const promise = new Promise(r => resolve = r);
    const unbind = this.bind(name, value => {
      resolve(value);
      unbind();
    });
    this._promises[name] = promise;
  }
  return this._promises[name];
};

/**
 * Sets value and dispatches event to force notify.
 *
 * @param {string} name Property name.
 * @param {?} value
 */
GrAttributeHelper.prototype.set = function(name, value) {
  this.element[name] = value;
  this.element.dispatchEvent(
      new CustomEvent(this._getChangedEventName(name), {detail: {value}}));
};