This appendix provides two lists of reserved keywords as defined in ECMAScript 5 (ES5). The first one is the current list of words, and the second is the list of words reserved for future implementations.

There's also a list of words that are no longer reserved, although they used to be in ES3.

You cannot use reserved words as variable names:

    var break = 1; // syntax error 

If you use these words as object properties, you have to quote them:

    var o = {break: 1};   // OK in many browsers, error in IE 
    var o = {"break": 1}; // Always OK 
    alert(o.break);       // error in IE 
    alert(o["break"]);    // OK