** You should simply use indexOf or some ... that's are JS 1.6 Array methods **

Array.prototype.has = function(obj) {
return this.indexOf(obj) !== -1;
};

Array.prototype.has = function(obj) {
return this.some(function(e){return e === obj});
};

** This implementation is for multiple search (more than one value that should be present) **

Array.prototype.has = function() {
var	i = arguments.length,
result = [];
while(i)
result.push(this.indexOf(arguments[--i]) !== -1);
return result.every(function(e){return e});
};

alert([1,2,3].has(3));	 //true
alert([1,2,3].has(2,4));	// false
alert([1,2,3].has(1,2,3));	// true