JavaScript Array function for unique elements

unique.js

/**
 * unique - Array function for unique elements
 * @use [2, 2, 3, 4, 3, 2].unqiue() // [2, 3, 4]
 */

Array.prototype.unique = function() {
    var unique = [];
    for (var i = 0; i < this.length; i++) {
        if (unique.indexOf(this[i]) == -1) {
            unique.push(this[i]);
        }
    }
    return unique;
};