javascript extend array

The .push method can take multiple arguments. You can use the spread operator to pass all the elements of the second array as arguments to .push:

>>> a.push(...b)
If your browser does not support ECMAScript 6, you can use .apply instead:

>>> a.push.apply(a, b)
Or perhaps, if you think it's clearer:

>>> Array.prototype.push.apply(a,b)