Callback funtions in Javascript

Question

Let's suppose we have

function first(){
  console.log(1);
}
function second(){
  console.log(2);
}
first();
second();

That will print

1
2

Now we put a timer inside the first() function.

function first(){
  // Simulate a code delay
  setTimeout( function(){
    console.log(1);
  }, 500 );
}
function second(){
  console.log(2);
}
first();
second();

Now this will give the opposite.

2
1

That's because Javascript is an event-driven language. My question is how to define a callback function in the above example, so as to wait and print

1
2

Thanks, Theo.

Either pass the second function to the first and let it execute it as callback, or let the first function return a promise whose completion you can await. — deceze, Jun 15 '20 at 07:44

score 0 · Answer 1 · answered Jun 15 '20 at 07:44

0

You just call second() inside first().

function first() {
  // Simulate a code delay
  setTimeout(function() {
    console.log(1);
    second();
  }, 500);
}

function second() {
  console.log(2);
}

first();

answered Jun 15 '20 at 07:44

holydragon

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Callback funtions in Javascript

1 Answers1