Answers for "Why do I get Cannot read property 'toString' or 'toUpperCase' of undefined"

Error: listen EADDRINUSE: address already in use :::3000

sudo lsof -i :3000

EADDRINUSE: address already in use

sudo lsof -i :<PORT>
kill -9 <PID>

EADDRINUSE: address already in use :::5000

sudo lsof -i :3000

EADDRINUSE: address already in use :::5000

kill -9 {PID}

Error: listen EADDRINUSE: address already in use

Find server pid:
	lsof -i tcp:5000 (the 5000 is the port number)
kill the server:
	kill -9 111119 (the 111119 is the pid)

Error: listen EADDRINUSE: address already in use :::3001

NODE PORT

Why do I get Cannot read property 'toString' or 'toUpperCase' of undefined

//To make sure that .toString() or .toUpperCase() doesn't throw an error,
you could:

string = "" + string; // amends the value to an string, even if its undefined or null etc
//instead of:
string = string.toString();