Object method loses its scope when called using setInterval

Question

Is there any way to print out the value of the array players like in the example below? I've tried to find a solution for hours now...

function Room(name, id, owner) {
    this.players = [];
    this.movementz =  function() {
        console.log(this.players);
    }
}

I'm calling the function using setInterval, like this:

setInterval(room.movementz, 1000);

Answer 1

The problem here is about the this object: creating your object and manually calling it's movementz method will work because the this element is the object itself, but using setInterval will cause the method to be called with this === window.

Here is an example:

var room = new Room();

room.movementz(); // []
setInterval(room.movementz, 1000); // undefined

This happens because when the movementz method gets called by setInterval, the this object is window, so, to fix this, you'll have to force the function to be called using room as this. You can easily accomplish this using the bind method, here's an example:

var room = new Room(),
    players = "hello";

setInterval(room.movementz, 1000);
// this will output "hello" because this === window

setInterval(room.movementz.bind(room), 1000);
// this will output [], because now this === room