Techniques for WCAG 2.0

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SCR18: Providing client-side validation and alert


Content that validates user input.

This technique relates to:


The objective of this technique is to validate user input as values are entered for each field, by means of client-side scripting. If errors are found, an alert dialog describes the nature of the error in text. Once the user dismisses the alert dialog, it is helpful if the script positions the keyboard focus on the field where the error occurred.


Example 1

The following script will check that a valid date has been entered in the form control.

Example Code:

<label for="date">Date:</label>
<input type="text" name="date" id="date" 
alert('This control is not a valid date. 
Please re-enter the value.');" />



For form fields that require specific input:

  1. enter invalid data

  2. determine if an alert describing the error is provided.

Expected Results

If this is a sufficient technique for a success criterion, failing this test procedure does not necessarily mean that the success criterion has not been satisfied in some other way, only that this technique has not been successfully implemented and can not be used to claim conformance.

Techniques are Informative

Techniques are informative—that means they are not required. The basis for determining conformance to WCAG 2.0 is the success criteria from the WCAG 2.0 standard—not the techniques. For important information about techniques, please see the Understanding Techniques for WCAG Success Criteria section of Understanding WCAG 2.0.