Method turns objects values into NaN. I guess it has something to do with 'this' keyword

Asked Oct 19 '17 at 21:34

Active Oct 19 '17 at 21:34

Viewed 28 times

I'm trying to write a timer in javascript for a little game using classes. For some reason function start() doesn't work and it's execution turns timer's values (s and cs) into NaN. Is there something wrong with this keyword?

class Timer
    {
        constructor()
        {
            this.s = 0;
            this.cs = 0;
        }

        start()
        {
            this.timerID = setInterval(function()
            {
                this.cs++;
                if (this.cs >= 100)
                    {
                        this.s++;
                        this.cs = this.cs % 100;
                    }}, 
                    10);
            }

        stop()
        {
            clearInterval(this.timerID);
        }
    }

Thanks in advance.

asked Oct 19 '17 at 21:34

cosine alpha

The value of `this` in your timer callback won't be the value it was in the context where the timer was established. – Pointy Oct 19 '17 at 21:35
Yup, use an arrow function instead – Vivick Oct 19 '17 at 21:37
Declare the `this` in a variable like `var _this = this;` and then use it. The setInterval has a different scope so the `this` points to something different. – nurdyguy Oct 19 '17 at 21:37
1

`var that = this;` is also quite conventional. – Kontsnor Oct 19 '17 at 21:39

Method turns objects values into NaN. I guess it has something to do with 'this' keyword

0 Answers0