Simple javascript searching

arraySearch.js

var MyNamespace = (function(namespace) {

	if (!Array.prototype.filter) {
	  Array.prototype.filter = function(fun /*, thisp */) {
		"use strict";

		if (this == null) throw new TypeError();

		var t = Object(this);
		var len = t.length >>> 0;
		if (typeof fun != "function") throw new TypeError();

		var res = [];
		var thisp = arguments[1];
		for (var i = 0; i < len; i++) {
		  if (i in t) {
			var val = t[i]; // in case fun mutates this
			if (fun.call(thisp, val, i, t)) res.push(val);
		  }
		}
		return res;
	  };
	}
	
	namespace.search = function(arr, query, field) {
		var re = new RegExp(query, 'i');
		return arr.filter(function(item) {
			if (field) 
				return re.test(item[field]);
			else 
				return re.test(item);
		});
	};

	return namespace;
})(MyNamespace || {});

tests.js

test( "simple array test", function() {
	var simpleArray = ['audi', 'acura', 'buick'];
	var result = MyNamespace.search(simpleArray, 'a');
	
  	ok( result[0] == 'audi' &&
  		result[1] == 'acura');
});


test( "collection test", function() {
	var collection = [
			{ make: 'audi', model: 'a4' },
			{ make: 'acura', model: 'TL' },
			{ make: 'buick', model: 'Skylark' }];
	var result = MyNamespace.search(collection, 'a', 'make');
	
  	ok( result[0] == 'audi' &&
  		result[1] == 'acura');
});

You don't have to write this.

if (typeof field != 'undefined')

You can just write this instead.

if (field)

I would also run it through a linter, like JSHint.

Everything else looks ok to me.