Cast javascript object to array. How to?

Question

I have made this sandbox test:

Answer 1

Use a for loop for max browser compatibility.

In Javascript all arrays are objects, but not all object are arrays. Take a look at this Perfection Kills page which describes how to check that something is an Array.

To check for an array, you can use Object.prototype.toString.call(theObject). This will return [object Array] for an object that is an Array and [object Object] for an object that's not an Array (see example below):

            function myLittleTest() 
            {
                var obj, arr, armap, i;    

                  // arr is an object and an array
                arr = [1, 2, 3, 5, 7, 11]; 

                obj = {}; // obj is only an object... not an array

                alert (Object.prototype.toString.call(obj));
                  // ^ Output: [object Object]

                obj = arr; // obj is now an array and an object

                alert (Object.prototype.toString.call(arr));
                alert (Object.prototype.toString.call(obj));
                  // ^ Output for both: [object Array]

                // works in IE
                armap = [];
                for(i = 0; i < obj.length; ++i)
                {
                    armap.push(obj[i] * obj[i]);
                }

                alert (armap.join(", ")); 

            }
            // Changed from prueba();
            myLittleTest();

jsFiddle example