EventListener

EventListener模块用于绑定或解绑事件，通过返回函数解绑事件。

'use strict';

var emptyFunction = require('./emptyFunction');

var EventListener = {
  // 非捕获模式绑定事件，返回值用于解绑事件
  listen: function listen(target, eventType, callback) {
    if (target.addEventListener) {
      target.addEventListener(eventType, callback, false);
      return {
        remove: function remove() {
          target.removeEventListener(eventType, callback, false);
        }
      };
    } else if (target.attachEvent) {
      target.attachEvent('on' + eventType, callback);
      return {
        remove: function remove() {
          target.detachEvent('on' + eventType, callback);
        }
      };
    }
  },

  // 捕获模式绑定事件，返回值用于解绑事件，IE不支持捕获模式
  capture: function capture(target, eventType, callback) {
    if (target.addEventListener) {
      target.addEventListener(eventType, callback, true);
      return {
        remove: function remove() {
          target.removeEventListener(eventType, callback, true);
        }
      };
    } else {
      if (process.env.NODE_ENV !== 'production') {
        console.error('Attempted to listen to events during the capture phase on a ' +
         'browser that does not support the capture phase. Your application ' 
         + 'will not receive some events.');
      }
      return {
        remove: emptyFunction
      };
    }
  },

  registerDefault: function registerDefault() {}
};

module.exports = EventListener;