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Idea #1
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(Step 1) If a load event occur with loadidx==1, then it is the first GForm load. Do nothing.

(Step 2) If a load event occur with loadidx==2, then it should be either reloading iframe or a form submition.

(Step 3) Set iframe.src to the initial URL.

	If that was reloading iframe, then nothing should happen because it's the same URL.
	Set timeout for 1 sec, then close the GForm with submission flag = 0.

	If that was a form submition, then another load event with loadidx==3 will occur.
	If loadidx==3, then close GForm with submission flag = 1
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In the above idea #1, the step 3 has a problem.
It's assuming that if you set iframe.src to the same URL, the iframe does nothing.
Actually it's wrong! Consider the following snipet.
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let loadidx=0;
el_iframe.addEventListener("load",function(){
	el_iframe.src="form-001.php"; // Assign the same URL as the initial URL

	loadidx++;
	console.log("loadidx",loadidx);
});
el_iframe.src="form-001.php";
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This code will get into an infinite loop because assigning the same URL will cause reloading!

However, the following code will not get into an infinite loop.
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let loadidx=0;
el_iframe.addEventListener("load",function(){
	el_iframe.src="form-001.php#abc";

	loadidx++;
	console.log("loadidx",loadidx);
});
el_iframe.src="form-001.php";
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The trick is appending fragments. In this case, the fragments are "#abc" 
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	el_iframe.src="form-001.php#abc";
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==>The trick won't work on remote URL!
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Suppose you set iframe to this URL
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	el_iframe.src="https://www.remote.com/test.php";
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Then set it to the URL with '#abc'
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	el_iframe.src="https://www.remote.com/test.php#abc";
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It will reload the entire page instead of just moving to '#abc'
because "https://www.remote.com/test.php" is remote URL.

It looks like there is no way to detect whether it's iframe reload or submitting.

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Then how about disabling the context menu so users can never reload the iframe?

==> Unfortunately, it's not possible to disable the context menu of an ifram that
contains an external web page.
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