Why is this code blocking?

is_return_evil_just_callbacks.js

var worker_clb = function(name, clb) {
  var d = new Date();
  for(var i = 0; i < 100000000; i++) {
    i+i;
  }
  clb(name + "_clb returns after " + ((new Date()) - d) + " ms.");
}

var a_lot_to_do = function(name, clb) {
  worker_clb(name, clb);
  clb(name + " is fired");
}



a_lot_to_do("w1", console.log);
a_lot_to_do("w2", console.log);
a_lot_to_do("w3", console.log);
a_lot_to_do("w4", console.log);

Output:

w1_clb returns after 221 ms.
w1 is fired
w2_clb returns after 223 ms.
w2 is fired
w3_clb returns after 221 ms.
w3 is fired
w4_clb returns after 221 ms.
w4 is fired

shouldn't it be like this?

w1 is fired
w2 is fired
w3 is fired
w4 is fired
w1_clb returns after 221 ms.
w2_clb returns after 223 ms.
w3_clb returns after 221 ms.
w4_clb returns after 221 ms.

No; Output is true! You're only one thread to run your code! so NodeJs runs "worker_clb" and next runs " clb(name + " is fired");". your code isn't async || non-blocking !