Extends an object or an array Returns Object or Array Extends the specified object or the array. If target is an array, then the source-N can only be an array too. It will perform a concatenation of arrays, cloning each item. If target is an object, then the source-N can only be objects and it will extend target with all keys in the source, cloning them. It is not a deep merge, but rather copy of top level keys cloning if they are objects var a = { c: 1, d: 2, k: { k1: 1, k2: 2 } } var b = w2utils.extend({}, a, { k: { k2: 5 } }) // there will be no b.k.k1 key in the target console.log(a.k.k2, b.k.k2);