js数组去重

Array.prototype.del = function(){ 
    var a = {}, c = [], l = this.length; 
    for (var i = 0; i < l; i++){ 
    var b = this[i]; 
    var d = (typeof b) + b; 
    if(a[d] === undefined){ 
        c.push(b); 
        a[d] = 1; 
    } 
}
    return c; 
}
//alert([1, 1, 2, 3, 4, 5, 4, 3, 4, 4, 5, 5, 6, 7].del());