can't use javaScript setInterval method

Question

i cant use setInterval mehod, i don't know why. what's wrong with this script, after clicking on stop it doesn't show the result of counter i in the text field.

<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
    <head>
        <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />

        <title>test_setInterval</title>

        <script type="text/javascript">
            var i = 0;
            var interval;

            function start ()
            {
                interval = document.setInterval("i++", 1000);
            }

            function stop ()
            {
                document.clearInterval(interval);
                output.value = i;
            }
        </script>

    </head>

    <body>
        <input id="output" type="text" />
        <input id="start" type="button" value="start" onclick="start()" />
        <input id="stop" type="button" value="stop" onclick="stop()" />
    </body>
</html>

bjornd · Accepted Answer · 2012-07-01 11:50:43Z

1

clearInterval and setInterval are methods of window, not document. You can call them as window.clearInterval or just clearInterval.
It's better to use function as the first argument for setInterval, not a string with the code, because eval is evil.

Here is a working demo http://jsfiddle.net/9cveg/

answered Jul 1, 2012 at 11:50

bjornd

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Comments

XCS · Accepted Answer · 2012-07-01 12:00:21Z

1

You have to wrap i++ inside a function.
Also, remove document. before the setInterval.
Now, be careful that this has a bug. If you press "start" twice, i will go up by two units every second.
Solved the bug by adding another clearInterval in the start function.

http://jsfiddle.net/46kzu/3/

    function start ()
    {   
        clearInterval(interval);
        interval = setInterval(function(){++i;}, 1000);

    }

    function stop ()
    {
        clearInterval(interval);
        output.value = i;
    }

edited Jul 1, 2012 at 12:00

answered Jul 1, 2012 at 11:54

XCS

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Comments

Ashwin Singh · Accepted Answer · 2012-07-01 11:57:13Z

0

According to definition, The setInterval() method calls a function or evaluates an expression at specified intervals (in milliseconds) and its window's method not document's .

 <script type="text/javascript">

                var i = 0;
                var interval;

                function start ()
                {
                    interval = window.setInterval("i++", 1000);
                }

                function stop ()
                {
                    document.clearInterval(interval);
                    output.value = i;
                }

            </script>

edited Jul 1, 2012 at 11:57

answered Jul 1, 2012 at 11:50

Ashwin Singh

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1 Comment

bjornd Over a year ago

This still won't work, setInterval will have 1 as a first argument not method which increments i.

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