Question

I just saw a expression from a JavaScript sample like following:

  var some = (x, y, z) + a;

what does it mean? and what is the result?

Answer 1

This is JavaScript’s comma operator

x, y, z; // is the same as
x;
y;
z; // this is the last thing returned, so
(x, y, z) === z;

Therefore, var some = (x, y, z) + a; is the same as var some = z + a;, except x and y are evaluated too.

It is useful if you want to shorten things to one line or need something evaluated before a second thing is available.