Onclick Change Hidden Field

I want to have it so it's

<input type="hidden" name="action" value="">
<input type="submit" value="Edit" onclick="DO THIS">

I want DO THIS to change the value of action to "edit"

How would I do this?

 

Now you're gettin' into DOM

First thing, you have to give your first input an id so you can reference it later (also, it's good standards compliance to end an input tag with a closing slash):

<input [B]id="action"[/B] type="hidden" name="action" value="" [B]/[/B]>

Code (markup):

Then modify the second input (not sure why you want an input for this; perhaps a link or a button might make more sense from a UI design point of view):

<input type="submit" value="Edit" onclick="[B]document.getElementById('action').value='edit';[/B]" [B]/[/B]>

Code (markup):