JavaScript testing for empty array, object keys

javascript-test-array

Javascript testing for empty (undefined) object or array

This is the problem, for JS object keys and for array's, not that I like really testing for undefined, I would rather set false or true and test for that, but ...;

var obj = { key: undefined };
obj["key"] != undefined // false, but the key exists!

and also;

if (urlobject[3] == 'undefined') {} // again does not work as expected

solution for keys;

!("key" in obj) // true if "key" doesn't exist in object
!"key" in obj   // ERROR!  Equivalent to "false in obj"

Or, if you want to particularly test for properties of the object instance (and not inherited properties), use hasOwnProperty:

obj.hasOwnProperty("key") // true

solution for array;

if ((typeof urlobject[3]) === 'undefined') {} // works as expected

Original source: http://stackoverflow.com/questions/1098040/checking-if-an-associative-array-key-exists-in-javascript