SharePoint does not have a PreCancelAction. I created what I needed for one project, and present it here for your creative uses and enhancements. No warranties and no support… but the price is right!
PreSaveAction
When you click Save from an ASPX list form SharePoint checks to see if you have added a PreSaveAction JavaScript function to the page. If you have included the function, it is called, your code run and then your code can return a True or False to allow the save to continue, or to cancel it. You can add this function directly to the page, via a Content Editor Web Part, and in 2013 as a JS Link. Do a web search to find examples of its use.
PreSaveAction sample:
<script type="text/javascript">
function PreSaveAction() {
// do pre-save work here: validation, messages, etc.
alert('Thank you for your suggestion!');
return true; // return true to continue with the save
// or return false to cancel the save
}
</script>
PreCancelAction
I needed a popup message to stress "Changes not saved", so I put together some JavaScript that intercepts the cancel and displays a message to the user.
All of the examples below look for INPUT tags with a VALUE of "Cancel". You may want to change this line to match your language requirements. The code also only intercepts INPUT tags that include "STSNavigate" in their onclick code. This is to avoid intercepting the attachment dialog's cancel button. The code stores all of the original onclick code in a globally scoped array named TTNoriginalFunctions as each Cancel button on the form may have had unique code.
Warn the user on cancel:
This example does not call your functions, it just intercepts the Cancel buttons and runs the imbedded alert code.
var TTNoriginalFunctions = [];
var TTNCounts = 0;
var TTNinputs = document.getElementsByTagName("input")
for (var i = 0; i<TTNinputs.length; i++)
{
if (TTNinputs[i].value == "Cancel")
{
if (TTNinputs[i].onclick)
{
if (String(TTNinputs[i].onclick).indexOf("STSNavigate")>-1)
{
TTNoriginalFunctions[TTNCounts] = TTNinputs[i].onclick;
TTNinputs[i].onclick = new Function(" return function () { alert('Changes not saved'); TTNoriginalFunctions[" + TTNCounts + "]();}")();
TTNCounts++;
}
}
}
}
Callable as a function:
This is the same as the above, but wrapped up in a function that you can call it from your code. You pass in the custom code to run as a string. This uses "new Function" to build the code from a string.
var TTNoriginalFunctions = [];
function TTNPreCancelAction(yourFunctionAsString)
{
var TTNCount = 0;
var TTNinputs = document.getElementsByTagName("input")
for (var i = 0; i<TTNinputs.length; i++)
{
if (TTNinputs[i].value == "Cancel")
{
if (TTNinputs[i].onclick)
{
if (String(TTNinputs[i].onclick).indexOf("STSNavigate")>-1)
{
TTNoriginalFunctions[TTNCount] = TTNinputs[i].onclick;
TTNinputs[i].onclick = new Function(" return function () { " + yourFunctionAsString + "; TTNoriginalFunctions[" + TTNCount + "]();}")();
TTNCount++;
}
}
}
}
}
TTNPreCancelAction("alert('changes not saved')");
A solution that works more like SharePoint's PreSaveAction:
You could add the TTNPreCancelAction function listed below to your master page or an existing linked JavaScript library. You can then add a PreCancelAction function to forms as needed using SharePoint Designer edits, Content Editor Web Parts or JS Link, just like the PreSaveAction functions. Your PreCancelAction function must return "true" or "false".
// Add this function to a form
function PreCancelAction()
{
alert('Changes not saved!'); return true;
//return confirm('Are your sure? Data will be lost!')
}
// Add this code to each form, or once in the master page.
var TTNoriginalFunctions = [];
var TTNCount = 0;
function TTNPreCancelAction()
{
var TTNinputs = document.getElementsByTagName("input")
for (var i = 0; i<TTNinputs.length; i++)
{
if (TTNinputs[i].value == "Cancel")
{
if (TTNinputs[i].onclick)
{
if (String(TTNinputs[i].onclick).indexOf("STSNavigate")>-1) // ignore the Attachments Cancel!
{
TTNoriginalFunctions[TTNCount] = TTNinputs[i].onclick;
TTNinputs[i].onclick = new Function(" return function () { if ('function'==typeof(PreCancelAction)) {if (!PreCancelAction()) {return false} }; TTNoriginalFunctions[" + TTNCount + "]();}")();
TTNCount++;
}
}
}
}
}
TTNPreCancelAction() //intercept the Cancel buttons
Have a better solution? Post a comment below! 
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