控制台日志记录 "this" returns "null"

Question

我正在尝试为我正在构建的 React 应用程序创建一个 flux 存储。我正在使用对象分配 polyfill npm 包和 Facebook 的 Flux 库。

最初我收到错误 "Cannot read property '_data' of null' error in the console which was refering to var currIds = this._data.map(function(m){return m.id;});. That method is currently the only one being called directly. I then did console.log(this) which returned "null"。

我觉得这很奇怪。怎么回事？

我的代码：

var Assign = require('object-assign');
var EventEmitterProto = require('events').EventEmitter.prototype;
var CHANGE_EVENT = 'CHANGE';

var StoreMethods = {

init: function() {},
set: function (arr) {
console.log(this);
    var currIds = this._data.map(function(m){return m.id;});

    arr.filter(function (item){
      return currIds.indexOf(item.id) === -1;
    }).forEach(this.add.bind(this));

},
add: function(item){
  console.log(this);
    this._data.push(item);
},
all: function() {
    return this._data;
},
get: function(id){
   return this._data.filter(function(item){
       return item.cid === id;
   })[0];
},
addChangeListener: function(fn) {
    this.on(CHANGE_EVENT, fn);
},
removeChangeListener: function(fn) {
    this.removeListener(CHANGE_EVENT, fn);
 },
 emitChange: function() {
    this.emit(CHANGE_EVENT);
 },
 bind: function(actionType, actionFn) {
    if(this.actions[actionType]){
        this.actions[actionType].push(actionFn);
    } else {
        this.actions[actionType] = [actionFn];
    }
}
};

exports.extend = function(methods) {
var store = {
_data: [],
actions: {}
};

Assign(store, EventEmitterProto, StoreMethods, methods);
store.init();

require('../dispatcher').register(function(action){
   if(store.actions[action.actionType]){
       store.actions[action.actionType].forEach(function(fn){
        fn.call(null, action.data);
       })   
   }
  });

  return store;
 };

Answer 1

我不能 see 在调用 set 的地方，但是你的 this 可以是 null 如果函数是通过 call 调用的（见 here) 或 apply，您的第一个参数是 null。这也发生在您的 require.register 回调中：

fn.call(null, action.data) //First parameter is your 'this'.

控制台日志记录 "this" returns "null"

Console logging "this" returns "null"

javascript

reactjs

browserify

babeljs

reactjs-flux