A script to automatically leave meetings / exit a webpage after a given amount of time

MeetingExiter.js

/* Run in your browser's JS console */
MeetingExiter = () => {
// Don't allow it to be running more than once
	if (typeof meetingExiterMutex !== "undefined") {
		if (meetingExiterMutex === true) {
			console.error("Cant't run more than 1 exiter job at a time!");
			return;
		} else {
	  		meetingExiterMutex = true;
	  	}
	} else {
		meetingExiterMutex = true; // No var/let means global
	}
	var mins = prompt("How many minutes from now would you like to leave the meeting?");
	if (mins === null) { // Prompt 'Cancel' button clicked
		meetingExiterMutex = false;
		return;
	}
	if (isNaN(mins) ||  mins === '') {
		meetingExiterMutex = false;
		console.error("Minutes must be a number!");
		return;
	}
	var confirm = prompt("Are you sure you want to exit in "+mins+" minutes? (Y/n)");
	// Null check 1st, so regex doesnt have to deal with it
	if (confirm === null || !confirm.match(/^[Yy]([Ee][Ss])?$/)) {
	    console.error("Job cancelled");
	    meetingExiterMutex = false;
	    return;
	}
	// Prevent "Leave site?" alert box from stopping the exit
	window.onbeforeunload = function(){};
	setTimeout(() => {
		/*  - /404 uses current host name so we avoid
			X-Frame-Options sameorigin security error
			- Don't use window.close() b/c you can get the error:
			"Scripts may only close the windows that were opened by them" */
		window.location.replace("/404");
	}, mins*60000); // Every min is 60000ms (60 secs/min, 1000ms/sec)
	console.clear(); // Clear other messages so its pretty
	console.log("%cExiting meeting in "+mins+" minute(s)!", 
		    "background: black; color: lime; font-size: 30px;");
}
MeetingExiter(); // Call func