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

问题描述

我在带有 harmony 标志的 Windows 上使用 node v0.11.14-nightly-20140819-pre.

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

我有一个 JavaScript 对象，它的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);
}

Service 对象的

serviceMethod 返回一个 promise.

serviceMethod of Service object returns a promise.

当我使用 User 对象时，如下所示:

When I use User object like below:

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

对象User的method2中的

this在被then调用时以undefined结束> 一旦兑现承诺.

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

我尝试同时使用 ES6 和 Bluebird 承诺实现.

I tried using both ES6 and Bluebird promise implementation.

为什么在这种情况下 this 最终是 undefined?

Why this ends up being undefined in this case?

推荐答案

为什么在这种情况下 this 最终是 undefined?

因为您传递的是函数，而不是绑定到实例的方法.这个问题甚至不是特定于 promise 的，请参见 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 将函数作为方法调用的另一种方式:

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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