To supplement benc's answer, see Standard ECMA-262. These are the official reserved words, but only a pedant ignores the implementation to respect the standard. For the reserved words of the most popular implementations, that is firefox and internet explorer, see benc's answer.

The reserved words in EMCAScript-262 are the Keywords, Future Reserved Words, NullLiteral, and BooleanLiterals, where the Keywords are

break do instanceof typeof case else new var catch finally return void continue for switch while debugger function this with default if throw delete in try

the Future Reserved Word​s are

abstract export interface static boolean extends long super byte final native synchronized char float package throws class goto private transient const implements protected volatile double import public enum int short

the NullLiteral is

null

and the BooleanLiterals are