This example shows how javascript determines if an array is duplicated. Share with you for your reference. The details are as follows:

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;
}

I hope this article has been helpful to your javascript programming.