The most accurate way to check JS object's type?

The JavaScript specification gives exactly one proper way to determine the class of an object:

Object.prototype.toString.call(t);

http://bonsaiden.github.com/JavaScript-Garden/#types

the Object.prototype.toString is a good way, but its performance is the worst.

http://jsperf.com/check-js-type

Use typeof to solve some basic problem(String, Number, Boolean...) and use Object.prototype.toString to solve something complex(like Array, Date, RegExp).

and this is my solution:

var type = (function(global) {
    var cache = {};
    return function(obj) {
        var key;
        return obj === null ? 'null' // null
            : obj === global ? 'global' // window in browser or global in nodejs
            : (key = typeof obj) !== 'object' ? key // basic: string, boolean, number, undefined, function
            : obj.nodeType ? 'object' // DOM element
            : cache[key = ({}).toString.call(obj)] // cached. date, regexp, error, object, array, math
            || (cache[key] = key.slice(8, -1).toLowerCase()); // get XXXX from [object XXXX], and cache it
    };
}(this));

use as:

type(function(){}); // -> "function"
type([1, 2, 3]); // -> "array"
type(new Date()); // -> "date"
type({}); // -> "object"

Accepted answer is correct, but I like to define this little utility in most projects I build.

var types = {
   'get': function(prop) {
      return Object.prototype.toString.call(prop);
   },
   'null': '[object Null]',
   'object': '[object Object]',
   'array': '[object Array]',
   'string': '[object String]',
   'boolean': '[object Boolean]',
   'number': '[object Number]',
   'date': '[object Date]',
}

Used like this:

if(types.get(prop) == types.number) {

}

If you're using angular you can even have it cleanly injected:

angular.constant('types', types);