referencing function from setInterval using Javascript

Question

When I try and run the add function it gives TypeError: this.add is not a function

function Timer(){
    this.t; 
    this.count = 0;

    this.start = function(){
        this.t = setInterval(function () {this.add()}, 1000);
    }
    this.add = function(){
        this.count++;
        console.log(this.count);
    }
}

function startTimer(){
    timer = new Timer();
    timer.start();
}

How am I able to access this.add function in that instance?

I'm reluctant to link to that other QA as it's full of answers which aren't the best one today. The accepted one, especially, wouldn't really help OP. — Denys Séguret, May 22 '15 at 13:10

score 3 · Accepted Answer · answered May 22 '15 at 13:07

3

A solution would be to create a variable to hold this but a simpler one is to use bind:

this.t = setInterval(this.add.bind(this), 1000);

answered May 22 '15 at 13:07

Denys Séguret

372,613
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score 1 · Answer 2 · answered May 22 '15 at 13:07

1

This happens because this inside your anonymous function get wrong context. You need to bind that function to your original context:

this.t = setInterval(function () {this.add()}.bind(this), 1000);

Or keep reference to your context inside some variable:

function Timer(){
    this.t; 
    this.count = 0;

    this.start = function(){
        var self = this;
        this.t = setInterval(function () {self.add()}, 1000);
    } 
...

answered May 22 '15 at 13:07

antyrat

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Don't you think there's a simpler solution ? ;) – Denys Séguret May 22 '15 at 13:09
I think your solution is simpler of course, but it depends on context and what OP will need in final result ;) – antyrat May 22 '15 at 13:10

referencing function from setInterval using Javascript

2 Answers2