In the words of Sitepoints Kevin Yank….

Your variable names can comprise almost any combination of letters and numbers, though no spaces are allowed.

Most punctuation and symbols have special meaning inside JavaScript, so the dollar sign ($) and the underscore (_) are the only non-alphanumeric characters allowed in variable names.

Variable names are also case-sensitive, so the names chameleon, Chameleon, and CHAMELEON refer to unique variables that could exist simultaneously.