javascript - setInterval function without arrow function

Question

I am learning about react components following the documentation https://facebook.github.io/react/docs/state-and-lifecycle.html

Why do we need to use arrow function here:

this.timerID = setInterval(() => this.tick(), 1000);

Why can't I just say (obviously it doesn't work)

this.timerID = setInterval(this.tick(), 1000);

Answer 1

The first argument for setInterval is of type function. If you write this:

this.timerID = setInterval(this.tick(), 1000);

…then you don't pass a function, instead you execute the function this.tick immediately and then pass the value returned by that function call as an argument.

You could write it like this:

this.timerID = setInterval(this.tick, 1000);

If you omit the parentheses, you pass a reference to your this.tick function, which is then executed by setInterval after 1000 milliseconds.