javascript mixin 访问对象 this

Question

我已经创建了一个对象和一个 mixin，我已经将 mixin 分配给对象，但是我似乎无法从 mixin 访问该对象，对吗？

mixin.js

module.exports = {
  doSomething: () => {
    let something = this.something.title;
  }
};

object.js

class Thing {   
  constructor(something) {
    this.something = something;   
  }

  _otherFunction() {
    // does stuff
  } 
}

module.exports = Thing;

index.js

const Something = require('./mixin');
const Thing = require('./Object');

Object.assign(Thing.prototype, Something);

然后当我实例化 Thing 并调用 doSomething() 时，它就无法访问 this.something... 所以

let thing = new Thing({title: 'abc'});
thing.doSomething();

我收到错误 Cannot read 属性 'title' of undefined

Answer 1

您需要放弃箭头函数，转而使用普通函数，因为箭头函数失去了 this 的作用域。

class Thing {   
  constructor(something) {
    this.something = something;   
  }
}

const mixin = {
  // changed arrow function to regular function
  doSomething: function () {
    console.log(this.something.title)
  }
}

const thing = new Thing({title: 'abc'})
Object.assign(thing, mixin)
thing.doSomething()

来自MDN: Arrow Functions：

An arrow function expression... and does not have its own this, arguments, super, or new.target.

很多人错误地认为箭头函数的唯一特点是语法更短——事实并非如此。它的主要实用功能是它不会创建自己的 this.

javascript mixin 访问对象 this

javascript mixin access to objects this

javascript

mixins

node.js