Javascript has a bunch of words with special meanings.

You've seen a number of them already, including:

var	function	if	else	while
continue	do	break	return	new
alert	ask	true	false	this

Your coding instincts probably tell you to avoid naming any of your variables or functions any of these words.

They're known as reserved words, and if you name any of your things using their names, chaos will ensue!