polygerrit-ui/app/elements/plugins/gr-event-helper/gr-event-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.
 */
import '../../../scripts/bundled-polymer.js';

const $_documentContainer = document.createElement('template');

$_documentContainer.innerHTML = `<dom-module id="gr-event-helper">
  
</dom-module>`;

document.head.appendChild($_documentContainer.content);

/** @constructor */
export function GrEventHelper(element) {
  this.element = element;
  this._unsubscribers = [];
}

/**
 * Add a callback to arbitrary event.
 * The callback may return false to prevent event bubbling.
 *
 * @param {string} event Event name
 * @param {function(Event):boolean} callback
 * @return {function()} Unsubscribe function.
 */
GrEventHelper.prototype.on = function(event, callback) {
  return this._listen(this.element, callback, {event});
};

/**
 * Alias of onClick
 *
 * @see onClick
 */
GrEventHelper.prototype.onTap = function(callback) {
  return this._listen(this.element, callback);
};

/**
 * Add a callback to element click or touch.
 * The callback may return false to prevent event bubbling.
 *
 * @param {function(Event):boolean} callback
 * @return {function()} Unsubscribe function.
 */
GrEventHelper.prototype.onClick = function(callback) {
  return this._listen(this.element, callback);
};

/**
 * Alias of captureClick
 *
 * @see captureClick
 */
GrEventHelper.prototype.captureTap = function(callback) {
  return this._listen(this.element.parentElement, callback, {capture: true});
};

/**
 * Add a callback to element click or touch ahead of normal flow.
 * Callback is installed on parent during capture phase.
 * https://www.w3.org/TR/DOM-Level-3-Events/#event-flow
 * The callback may return false to cancel regular event listeners.
 *
 * @param {function(Event):boolean} callback
 * @return {function()} Unsubscribe function.
 */
GrEventHelper.prototype.captureClick = function(callback) {
  return this._listen(this.element.parentElement, callback, {capture: true});
};

GrEventHelper.prototype._listen = function(container, callback, opt_options) {
  const capture = opt_options && opt_options.capture;
  const event = opt_options && opt_options.event || 'click';
  const handler = e => {
    if (e.path.indexOf(this.element) !== -1) {
      let mayContinue = true;
      try {
        mayContinue = callback(e);
      } catch (e) {
        console.warn(`Plugin error handing event: ${e}`);
      }
      if (mayContinue === false) {
        e.stopImmediatePropagation();
        e.stopPropagation();
        e.preventDefault();
      }
    }
  };
  container.addEventListener(event, handler, capture);
  const unsubscribe = () =>
    container.removeEventListener(event, handler, capture);
  this._unsubscribers.push(unsubscribe);
  return unsubscribe;
};