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Javascript - Enable and Disable form elements

Article by:  Jeff Anderson  ( 1362 ) (3/6/2002)
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Summary: This is a relatively little known and under-used feature of javascript which can be very useful in guiding a user through a form. Using the disabled tag, you can switch on and off elements in a form.
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This is a relatively little known and under-used feature of javascript which can be very useful in guiding a user through a form. Using the disabled tag, you can switch on and off elements in a form.

Here is a standard text field:



Now here it is again, disabled:



Try typing in the second box, and you'll see that you can't - it's been disabled. You can do the same any other elements in a form - checkboxes, selection boxes and the rest.

Disabling Form Elements - Common Uses

One common use of this is to only enable the element, once the appropriate field has been selected earlier in the form.

Now here's a practical example. The 'explain your choice' field only becomes enabled when I have selected the answer to Question 1. Before selecting a radio button, try typing in the text field - you can't!

Question 1
Answer a:
Answer b:

Explain your choice:



Disabling Form Elements - How it's done

To disable an element, put the phrase disabled="true" within the element tag.



Once you've set the disabled tag, you can enable it using something like the following code:


 
<script language="javascript">

function enableField()
{
document.form1.address2.disabled=false;
}
 
</script>

<a href="javascript:enableField()">Click here to enable the element<a/>



With disabled set to false, the form element becomes useable.






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