How do I combine Javascript Classes and Callbacks properly?

Question

This isn't my actual code (hopefully obviously), but it's a very short example that demonstrates the problem.

I'm writing a class with a method that accepts a callback as an argument. When the method finishes, it should call the callback.

class Demo {
    constructor() {
        this.method1();
    }

    method1() {
        console.log("Method1");
        this.method2(this.method1);
    }

    method2(onDone) {
        console.log("Method2");
        onDone();
    }
}

new Demo();

So I want this to jump back and forth between calling method1 and method2. If it worked properly, I should end up with a stack overflow, but instead what happens is this:

Method1
Method2
Method1
Uncaught TypeError: Cannot read property 'method2' of undefined
  at method1 (demo.js:8)
  at Demo.method2 (demo.js:13)
  at Demo.method1 (demo.js:8)
  at new Demo (demo.js:3)

Somehow, when we enter method1 the second time its been forgotten that this is an instance of Demo. I tried replacing onDone() in method2 with this.onDone() but then it completely fails to find onDone (which makes sense - onDone is the name of an argument, not the name of a member of Demo.)

What is the proper way of doing this?

That question doesn't involve javascript's `class` keyword. It may have the same root issue, but it's certainly not a duplicate of this one. — ArtOfWarfare, Oct 08 '17 at 15:56
Use `this.method2(this.method1.bind(this));` or use `onDone.call(this);` — 4castle, Oct 08 '17 at 15:59

How do I combine Javascript Classes and Callbacks properly?

0 Answers0