Avoid "use strict" (ES5+), Object.create , Object.defineProperty , getters/setters, and JSON (unless you include a polyfill). Stick to var , function declarations, for loops, in checks with hasOwnProperty , and simple object literals for cross-browser safety.
(since ES3 arrays don’t have it either): es3 edit
if (!Array.prototype.indexOf) Array.prototype.indexOf = function (searchElement, fromIndex) var i; for (i = (fromIndex ; Avoid "use strict" (ES5+), Object