this.async()在JavaScript中做什么 [英] What does this.async() do in JavaScript

问题描述

继续在代码中看到这种模式，但是在google或SO中找不到对该模式的任何引用，这很奇怪.有人可以指出我要参考的this.async()函数吗?

Kept on seeing this pattern in code, but couldn't find any reference to it in google or SO, strange. Can someone point me to reference for this.async() function?

  var done = this.async();
  // ...
  $.get(path, function(contents) { // or some other function with callback
    // ...
    done(JST[path] = tmpl);
  })

推荐答案

这是解决this在回调内部转义的方法.没有此额外参考，代码将如下所示:

It is a way to work around the problem of this escaping inside callback. Without this extra reference the code would look like this:

$.get(path, function(contents) { // or some other function with callback
  //Wrong! `this` might no longer point to your object
  this.done(JST[path] = tmpl);
})

不幸的是！响应回调内部的this与外部的this不同.实际上，它可以是任何东西，具体取决于$.get(使用调用回调)决定它是什么.大多数人出于相同目的使用名为that的额外引用:

Unfortunately! this inside response callback is not the same as this outside of it. In fact it can be anything, depending on what $.get (calling the callback using) decides it to be. Most of the people use extra reference named that for the same purpose:

var that = this;
// ...
$.get(path, function(contents) { // or some other function with callback
  // ...
  that.async(JST[path] = tmpl);
})

这种模式似乎也是合理且可读的.

This pattern also seems reasonable and readable.

哦，如果您对此语法感到好奇:

Oh, and if you are curious about this syntax:

done(JST[path] = tmpl)

这是一个用作表达式的赋值.赋值的值在右侧，因此此代码等效于:

This is an assignment used as an expression. The value of assignment is the right-hand side, so this code is equivalent to:

JST[path] = tmpl;
done(tmpl);

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