setTimeout to detect changes in a text field

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

XML

<!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/

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.

Posted 27-Nov-12 9:28am

RainLover

Updated 27-Nov-12 21:35pm

v2

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Comments

ZurdoDev 27-Nov-12 15:39pm

What doesn't work right about it?

RainLover 28-Nov-12 3:41am

Just updated my question for clarification.

ZurdoDev 28-Nov-12 7:50am

But it worked fine for me. I still don't see what the issue is.

RainLover 28-Nov-12 11:07am

Please let me provide two examples:
1. Enter a sentence/code into the text field. Then select/highlight it. Now press the 'Delete' button on your keyboard. You won't see the same change on the iframe unless the textarea loses focus.
2. Enter a sentence and then delete all the letters using the 'backspace' key. You'll see the last letter remains in the iframe.
As I said 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. Something like this:

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

ZurdoDev 28-Nov-12 11:14am

Have you tried the onchange event?

RainLover 28-Nov-12 11:40am

The onchange event only works when the text field loses focus.

ZurdoDev 28-Nov-12 11:45am

try the onkeydown event. http://www.w3schools.com/tags/ref_eventattributes.asp

RainLover 28-Nov-12 11:46am

It doesn't cover the changes made by mouse.

ZurdoDev 28-Nov-12 11:53am

Yes, but if you refer to that url, there are other events, including mouse events. Depending on how complicated your form is, it may just be easier to have it always running. Also, you could probably set your timeout value to 100 and still have a good user experience but then it is running 10 times less often if you had it continually looping.

R. Giskard Reventlov 27-Nov-12 18:50pm

I wonder why you wonder why?

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