在setTimeout上使用Apply / call而不是bind

Question

I've been working with asynchronous functions

I've finally got around to avoid var _this = this; and switched to actually using call/apply . However when doing this,

/* inside instantiated obj */
setTimeout(function(){ 
  /* more code here */ 
}.apply(this), 0);

,does not launch an error and seems to work. Why? Because I recently noticed that it was "wrong" and should actually be:

/* inside instantiated obj */
setTimeout(function(){ 
  /* more code here */ 
}.bind(this), 0);

The bind() method creates a new function that, when called, has its this keyword set to the provided value, with a given sequence of arguments preceding any provided when the new function is called.

Answer 1

When you call apply or call methods on a function object, they will be invoked immediately and only the result is passed to the setTimeout .

But bind returns a new function object and that will be invoked after the timeout elapses.

Since the timeout is set to 0, both the setTimeout s wait only 0 milliseconds and so you don't see any difference.

---

You can use this example to understand it better.

console.log(new Date());

setTimeout(function () {
    console.log("Apply", new Date());
}.apply(this), 3000);

setTimeout(function () {
    console.log("Bind", new Date());
}.bind(this), 3000);

You should be able to observe 3 seconds difference between Bind 's and the other two.