setTimeout to detect changes in a text field

JavaScript
1

I wonder why the following sample code doesn’t work properly:

<!DOCTYPE html>
<html>

    <head>
        <title></title>
        <style type="text/css">
            textarea, iframe {
                display:block;
                width:300px;
                height:100px;
                margin:3px;
                padding:3px;
                border:1px solid #CCC;
            }
        </style>
    </head>

    <body>
        <textarea id="field" onfocus="getFocus();" onblur="loseFocus();">This is some text.</textarea>
        <iframe name="target"></iframe>
        <script>
            var textarea = document.getElementById('field');
            var iframe = window.target.document;

            function displayResult() {
                if (textarea.value) {
                    iframe.open();
                    iframe.write(textarea.value);
                    iframe.close();
                }
                window.setTimeout(displayResult, 10);
            }

            function getFocus() {
                if (textarea.value == textarea.defaultValue) {
                    textarea.value = '';
                }
            }

            function loseFocus() {
                if (textarea.value == '') {
                    textarea.value = textarea.defaultValue;
                }
            }
            displayResult();
        </script>
    </body>

</html>

Demo: http://jsfiddle.net/RainLover/4ksMR/

2

Howdy,

You need to pass a function to setTimeOut.

In other words, change this:

window.setTimeout(displayResult, 10);

to this:

window.setTimeout(function(){displayResult()}, 10);

and things will work as expected.

3

Both of those code samples are passing a function to setTimeout - just the one the OP is using is shorter than your replacement as it calls the function directly instead of ccalling an anonymous function that then calls the function.

I can’t see exactly where the problem is but suspect it probably relates to the iframe part of the code.

4

The OP seems to have the demo working now if you look at the Fiddle.
I can’t work out what’s different though.

5

The iframe content is supposed to get updated in real time – as soon as the textarea content changes by keyboard or mouse. This approach is an alternative to the oninput event. But since oninput isn’t well-supported across different browsers I decided to create a timer to compare the current text field value with its value in 10 milliseconds before.