How to expand JavaScript Array with another Array?

Question

There doesn't seem to be a way to expand a JavaScript Array with another Array, i.e. to emulate Python's extend method.

What I want to achieve is the following:

>>> a = [1, 2]
[1, 2]
>>> b = [3, 4, 5]
[3, 4, 5]
>>> SOMETHING HERE
>>> a
[1, 2, 3, 4, 5]

I know there's a a.concat(b) method, but it creates a new array instead of simply extending the first one. I'd like an algorithm that works efficiently when a is significantly larger than b (i.e. one that does not copy a).

Answer 1

The best I came up with so far is:

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

but it feels a little like a hack. Any other suggestions?

Answer 2

Did u try it by using splice method ?

Answer 3

concat will be the one you want:

>>> a = [1, 2]
[1, 2]
>>> b = [3, 4, 5]
[3, 4, 5]
>>> a = a.concat(b)
>>> a
[1, 2, 3, 4, 5]

Edit: just saw your note about concat. In that case your a.push.apply(a, b) is going to be the most efficient.

Answer 4

It is possible to do it using splice():

b.unshift(b.length)
b.unshift(a.length)
Array.prototype.splice.apply(a,b) 
b.shift() // restore b
b.shift() //

But despite being uglier it is not faster than push.apply, at least not in Firefox 3.0. Posted for completeness sake.