js去除数组里重复数据

//去除数组里的重复  
    Array.prototype.distinct = 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;  
    }  
  
 var ColorArr = ["X", "X", "M"];  
 var ItemColor = ColorArr.distinct();  
console.log(ItemColor);