JavaScript：函数字典：函数可以从其字典中引用函数吗？

Question

In the code below, when somethingUseful.thisUsefulThing is called from setTimeout , can it reference somethingUseful.thatUsefulThing ?

var somethingUseful = {
  thisUsefulThing: function() {
    this.thatUsefulThing();
  },

  thatUsefulThing: function() {
    console.log("I am useful!");
  }
}

setTimeout(somethingUseful.thisUsefulThing, 1000);

Right now, I am getting this error:

Uncaught TypeError: Object [object global] has no method 'thatUsefulThing'

Answer 1

To simply answer your question, YES, thisUsefulThing CAN access thatUsefulThing

But as your code currently runs, 'this' is not actually global, it is a reference to somethingUseful to all direct descendants itself.

When I am working with literal objects, I usually reference them by name rather than with 'this', so in your case I would replace 'this.thatUsefulThing()' with somethingUseful.thatUsefulThing()

Why? Because it works globally, anyway!

EDIT:

As plalx pointed out in his comment to my answer, best practices for implementing this class (with an example class member) would use functional classes / prototypes and look something like this:

function SomethingUseful () {
    this.member = 'I am a member';
}
SomethingUseful.prototype.thisUsefulThing = function () {
    this.thatUsefulThing();
}
SomethingUseful.prototype.thatUsefulThing = function () {
    console.log('I am useful, and ' + this.member);
}
usefulObject = new SomethingUseful();

usefulObject.thisUsefulThing(); // logs fine with access to this.member
setInterval(usefulObject.thisUsefulThing.bind(usefulObject), 1000); // has access to this.member through bind()

Answer 2

只需this值绑定到somethingUseful 。

setTimeout(somethingUseful.thisUsefulThing.bind(somethingUseful), 1000);