How do you force a script to fire on Page Not Found?

[markschmucker (Mark S)]

Continuing the discussion from How do you force a script to refire on every page load in Discourse?:

@Zyniker

I am currently attempting to use this API to trigger a redirection from a category to an external site…

<script type='text/discourse-plugin' version='0.8.19'>
$( document ).ready(function() {
	if ( window.location.href === "https://omnifora.com/c/redirect-politifora" ) {
		window.location.replace( "https://politifora.com/" );
	}
});
</script>

As discussed in the now-closed topic, the code above does fire when a topic is loaded. But I want to trigger a redirection when the Page Not Found page is loaded. Neither api.onPageChange nor $( document ).ready fire on a 404 error. How can I catch a 404 and redirect?