I don't get the non-blocking description

[johnyradio]

Hi, i don't get the section on non-blocking code. You say a must complete it's task before it calls b -- to me, that sounds like a is blocking b. I thought asynchronous means two threads of code, a and b, getting executing simultaneously, not first a, then b. Or that b can begin before a is finished. -thx

[benjick]

A is blocking b because you want to use the result of a inside b. Nothing else is blocked and other script can execute

[jGlass314]

I think this section needs some work. The only reason this is non-blocking is because a() calls another function download that defines a function with the callback to b(). The description however implies you could define a() simply as:

function a(done) {
  done();
};

and execution would be asynchronous.

However, if a() were defined this way and you called functions:

a(b);
c();

then c() wouldn't get called until b() finished inside of a(), and a() would block c()'s execution after all.