ES6 / Bluebird承诺的对象方法 [英] Object method with ES6 / Bluebird promises

问题描述

我在Windows上使用节点v0.11.14-nightly-20140819-pre harmony flag。

I am using node v0.11.14-nightly-20140819-pre on Windows with harmony flag.

我有一个JavaScript对象，其原型中定义了两个方法：

I have JavaScript object with two methods defined in its prototype:

function User (args) {
    this.service= new Service(args);
}

User.prototype.method2 = function (response) {
    console.log(this); // <= UNDEFINED!!!!
};

User.prototype.method1 = function () {
    .............
    this.service.serviceMethod(args)
        .then(this.method2)
        .catch(onRejected);
};

function onRejected(val) {
    console.log(val);
}

serviceMethod of 服务对象返回一个承诺。

serviceMethod of Service object returns a promise.

当我使用用户对象如下：

let user = new User(args);
user.method1();

此 in 对象的method2 用户在调用时结束 undefined 然后一旦履行承诺。

this in method2 of object User ends up undefined when called by then once promise is fulfilled.

我尝试使用 ES6 和 Bluebird 承诺实施。

I tried using both ES6 and Bluebird promise implementation.

为什么这个在这种情况下最终是 undefined ？

Why this ends up being undefined in this case?

推荐答案

为什么此最终为 undefined 在这种情况下？

Why this ends up being undefined in this case?

因为你传递了一个函数，而不是一个方法绑定到一个实例。此问题甚至不是特定于承诺的，请参阅如何在回调中访问正确的`this`上下文？解决方案：

Because you're passing a function, not a method-bound-to-an-instance. This problem is not even promise-specific, see How to access the correct `this` context inside a callback? for the generic solution:

….then(this.method2.bind(this))… // ES5 .bind() Function method

….then((r) => this.method2(r))… // ES6 arrow function

但是， Bluebird确实提供了另一种方法来调用该函数作为一种方法：

However, Bluebird does offer an other way to call the function as a method:

this.service.serviceMethod(args)
    .bind(this)
    .then(this.method2)
    .catch(onRejected);

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