Check if an argument is an Array in javascript

var isArray(obj){
   if(obj.constructor.toString().indexOf(‘Array’)!=-1) {
       return true;
   } else {
       return false;
   };
}

Tips:
You can alert(obj.constructor);
to see the string value.
Similarly, you can check if an argument is an function with following
code:

var isFunction(obj){
   if(obj.constructor.toString().indexOf('Function')!=-1){
       return true;
   } else {
       return false;
   }
};