Question

What’s the ‘right’ way to tell if an object is an Array?

function isArray(o) {
???
}

Answer 1

The best way:

function isArray(obj) {
  return Object.prototype.toString.call(obj) == '[object Array]';
}

The ECMAScript 5th Edition Specification defines a method for that, and some browsers, like Firefox 3.7alpha, Chrome 5 Beta, and latest WebKit Nightly builds already provide a native implementation, so you might want to implement it if not available:

if (typeof Array.isArray != 'function') {
  Array.isArray = function (obj) {
    return Object.prototype.toString.call(obj) == '[object Array]';
  };
}