Why doesn't this simple JavaScript increment and decrement method work?

Question

(function() {
    var count = {
        digit: 0,
        increment: function() {
            var interval = setInterval(function() {
                if (++count.digit == 10) {
                    clearInterval(interval);
                    count.decrement();
                }
                var update = document.getElementById("liveUpdate");
                update.innerHTML = count.digit;
            }, 500);
        },
        decrement: function() {
            var interval = setInterval(function() {
                if (--count.digit == -1) {
                    clearInterval(interval);
                }
            }, 500);
        }
    };
    count.increment();
})();

It stops but it doesn't go down? What could be the problem?

Your code is correct, but you forget to display the `digit` in the `update` element. — jerone, Mar 20 '11 at 11:33

score 4 · Accepted Answer · answered Mar 20 '11 at 11:29

Your decrement function never updates the output anywhere. The variable is going down but you don't show that on screen.

Try (or check the corresponding JSFiddle):

(function() {
    var update = document.getElementById("liveUpdate");
    var count = {
        digit: 0,
        increment: function() {
            var interval = setInterval(function() {
                if (++count.digit == 10) {
                    clearInterval(interval);
                    count.decrement();
                }
                update.innerHTML = count.digit;
            }, 500);
        },
        decrement: function() {
            var interval = setInterval(function() {
                if (--count.digit == -1) {
                    clearInterval(interval);
                }
                update.innerHTML = count.digit;
            }, 500);
        }
    };
    count.increment();
})();

score 2 · Answer 2 · edited May 23 '17 at 12:11

2

setInterval will call the function every 500 seconds. It will not stop until you stop it. You can read more about stopping it at Stop setInterval call in JavaScript

edited May 23 '17 at 12:11

Community

1
1

answered Mar 20 '11 at 11:18

Peeter

9,282
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score 2 · Answer 3 · answered Mar 20 '11 at 11:20

2

It't not a bug, it's a feature ;-). setInterval() runs the given function in a loop with a given interval (500 ms). See this article for details.

answered Mar 20 '11 at 11:20

Tomasz Nurkiewicz

334,321
69
703
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Why doesn't this simple JavaScript increment and decrement method work?

3 Answers3