Ever since ECMAScript 3 was defined, one of the classic problems has been truly determining whether a given object is an array. When dealing with a single web page, and therefore a single global scope, the instanceof operator works well:
if (value instanceof Array){
//do something on the array
}The one problem with instanceof is that it assumes a single global execution context. If you are dealing with multiple frames in a web page, you’re really dealing with two distinct global execution contexts and therefore two versions of the Array constructor. If you were to pass an array from one frame into a second frame, that array has a different constructor function than an array created natively in the second frame. To work around this problem, ECMAScript 5 introduced the Array.isArray() method. The purpose of this method is to definitively determine if a given value is an array regardless of the global execution context in which it was created. Example usage:
if (Array.isArray(value)){
//do something on the array
}