javascript，promises，如何在当时范围内访问变量 [英] javascript, promises, how to access variable this inside a then scope

问题描述

我希望能够在 .then 范围内调用一个函数，为此我使用 this.foo（）方式。但如果我在 .then 中执行此操作，则会出现错误，因为此似乎已丢失。我该怎么办？

I want to be able to call a function inside the .then scope, and for that I use the this.foo() manner. But if I do this inside the .then I get an error, since this appears to be lost. What can I do?

在这段代码中，这相当于对象具有相同的输出

In this code, this would be equivalent to have the same output for the object this

console.log(this)
one().then(function() {
  console.log(this)
})

function one() {
  var deferred = $q.defer();
  deferred.resolve()
  return deferred.promise;
}

这似乎都不起作用

console.log(this)
var a = this;
one().then(function(a) {
  console.log(a)
})

推荐答案

你的第二个代码示例是正确的方法。由于新功能的范围发生了变化，此也会发生变化，因此您可以引用这个在函数之外。

Your second code example is the right way to go. Because the scope changes in the new function, this changes too, so you're right to make a reference to this outside of the function.

它失败的原因是因为函数使用了你传递给函数的 a 而不是你在它之外定义的全局 a 。

The reason it failed is because the function is using a that you passed into the function rather than the global a you defined outside it.

换句话说：

var a = this;
one().then(function () {
  console.log(a)
});

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