How to duplicate elements in a js array?

Question

Whats the easiest way (with \"native\" javascript) to duplicate every element in a javascript array?

The order matters.

For example:

Answer 1

Basically:

a = [2, 3, 1, 4];
b=[];

for(var i = 0; i< a.length;++i){
  b.push(a[i]);
  b.push(a[i]);
}

a=b;