Is it possible to determine if an object created with Object.create inherits from Array in JavaScript?

Question

Identifying which objects are which is complicated in JavaScript, and figuring out which objects are arrays has something of a hacky solution. Fortunately, it manages to wor

Answer 1

ECMAScript 5 has introduced Array.isArray() into javascript which provides a reliable way to check. For older browsers, we fix that by (quoted from this book)

function isArray(value) {
    if (typeof Array.isArray === "function") {
         return Array.isArray(value);
    } else {
         return Object.prototype.toString.call(value) === "[object Array]";
    }
}

But i just found out the built-in function Array.isArray does not work correctly when we use Object.create (tested in chrome). I came up with a method that works:

function isArray(value) {
     if (typeof value === "undefined" || value === null) {
          return false;
     }
     do {
          if (Object.prototype.toString.call(value) === "[object Array]") {
               return true;
          }
          value= Object.getPrototypeOf(value);
     } while (value);

     return false;
}

Use it:

var arr = Object.create(Array.prototype);
var arr1 = Object.create(Object.create(Array.prototype));
var arr2 = new Array();
var arr3 = [];
isArray(arr); 
isArray(arr1); 
isArray(arr2); 
isArray(arr3);