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Chapter 6. Scripting Events > Event Handler Return Values

6.3. Event Handler Return Values

A few event handlers associated with specific objects have extra powers available to them, based on whether the event handler contains a scripted return statement that returns true or false. For example, an onClick event handler associated with a link ignores the action of the HREF and TARGET attributes if the event handler evaluates to return false. Similarly, a form object's onSubmit event handler can cancel the submission of a form if the event handler evaluates to return false.

The easiest way to implement this feature is to include a return statement in the event handler itself, while the function invoked by the handler returns true or false based on its calculations. For example, if a form requires validation prior to submission, you can have the onSubmit event handler invoke the validation routine (probably passing this, the form itself, as a parameter to the function). If the routine finds a problem somewhere, it returns false and the submission is canceled; otherwise, it returns true and the submission proceeds as usual. Such a FORM element looks like the following:


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