JS class method in a setInterval doesn't work

Question

I have this simple example with a class with a setInterval that calls main() every 5 seconds. When it comes to call print() it returns me TypeError: this.print is not a function. And I'm really stuck. Why if I call main() without setInterval it works smoothly but with setInterval it fails? It's weird. Any workaround to call main() periodically without this issue?

"use strict";

class test {
  constructor() {
      this.interval = setInterval(this.main, 5000);
  }

  print(){
      console.log('Teeeessssttt');
  }

  main(){
      this.print();
  }
}

const a = new test();

score 8 · Answer 1 · answered Jul 28 '18 at 14:07

8

You'll need to use bind:

this.interval = setInterval(this.main.bind(this), 5000);

answered Jul 28 '18 at 14:07

Andy Gaskell

31,495
6
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Can you give a few explanations? – GHopper Jul 28 '18 at 14:12
Thank, that worked. I'll study more about .bind because it is not yet clear why that works :) – Michele Tuloski Furci Jul 28 '18 at 14:13
Also read the [setInterval](https://developer.mozilla.org/en-US/docs/Web/API/WindowOrWorkerGlobalScope/setInterval) documentation. In your original code `this.main` was being called from global scope, so `this` was either the window object if you're running in a browser or the global object if you're running in node. – Andy Gaskell Jul 28 '18 at 14:19

score 0 · Answer 2 · answered Jul 28 '18 at 14:12

0

You can try setInterval(() => this.main(), 5000) as well. this in JavaScript can differ than what you'd expect the program's source code to suggest. See MDN's take on this.

answered Jul 28 '18 at 14:12

Horia Coman

8,681
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JS class method in a setInterval doesn't work

2 Answers2