Question

I have 2 functions. The second one is faster than the first one,how could the function wait to complete first one’s work?

function1(); // slow 

function2(); // fast

Answer 1

JavaScript is imperative and single-threaded, it just works like this. function2() won’t start until function1() finishes.

If by slow you mean calling asynchronously some external service via AJAX, then we’re talking. function1() must provide some sort of callback so that when asynchronous request finishes, function2() is called:

function1(function2);

The implementation is trivial, e.g. using jQuery:

function function1(callback) {
  $.ajax({url: 'some-url'}).done(callback);
}