Entry
How to ensure a FORM is only submitted once?
this.submitted is already true, why do we still need disableSubmit(this)?
Apr 23rd, 2003 14:07
Nel MS, Aral Balkan, Martin Honnen, Hanh Huynh, Nel MS
The easiest way to make sure forms are submitted only once: Disabling
the SUBMIT button after clicking it once.
An innocent button that is clickable (see below). Now when a user
clicks once (onClick), this button (this.) will be disabled
(disabled=true).
<input type="submit" onClick="this.disabled=true">
The [disabled] tool can be used on tables as well. IE. Put a bunch of
buttons in a table and assign the table (or TD) an
onClick="this.disabled=true" and see what happens!!
(Nel MS)
=====================================================================
Author: Billy Cook (64.89.82.101)
Date: 2020-08-28 06:28:41
When printing out the form I store a random number in a session
variable and put a hidden field in the form with the same random
number
as its value. When processing the form submission I compare the value
of the hidden field in the form with the one in the session. If they
don't match then I don't process the form. If they do match I process
the form and unregister the variable from the session. If a user tries
to re-post the form the value in the session will no longer match the
hidden field in the form.
***
To add to Billy's method: If you want to have a page that may get
resubmitted (but not in the same state twice -- ie, via refresh) then
use not a random number for the session variable but a counter. Store
that counter in your form in a hidden field and check for it at the
start of your script. If the page is submitted via a form submit
button, then the value of the hidden field will equal the value of
your
session variable (the counter), if the form was submitted via the
Refresh button on the browser then it will not. Here's how it works
(only the pertinent parts / pseudo-code):
Page first loads:
-----------------
$sessionVar = 0;
// ... echo '<form>... etc.
echo '<input type="hidden" name="hiddenFormVar"
value="'.$sessionVar.'">;
User submits via the submit button in the form:
-----------------------------------------------
at start of script => $sessionVar == 0 == $hiddenFormVar // ok,
process
form
++$session_var; // increment the counter
// ... echo '<form>... etc.
echo '<input type="hidden" name="hiddenFormVar"
value="'.$sessionVar.'">; // write out the new session_var
User presses the Refresh button:
--------------------------------
at start of script => ($sessionVar == 1) != ($hiddenFormVar == 0) //
not, ok -- do not process
That simple, really! Hth. Aral :)
***
You might want to prevent users from trying to submit the same form
twice (or even more often) for instance when they have already
submitted but processing takes slows and they impatiently hit the
submit button again.
You can use the <FORM ONSUBMIT handler to save a flag that the form
got
already submitted:
<HTML>
<HEAD>
<SCRIPT>
function disableSubmits (form) {
for (var i = 0; i < form.elements.length; i++)
if (form.elements[i].type.toLowerCase() == 'submit')
form.elements[i].disabled = true;
}
</SCRIPT>
</HEAD>
<BODY>
...
<FORM ACTION="whatever"
TARGET="_blank"
ONSUBMIT="if (this.submitted) return false; else {
this.submitted
= true; disableSubmits(this); return true; }"
>
