What my code display this?

Question

I've just started learning javascript and I've write a code that display at the end of the output undefined? why?

var laugh = function laughs(y) {

  while (y > 0) {

    console.log("ha");
    y--;

  }

  console.log("ha!");
}

console.log(laugh(10));

And this is the output:

ha
ha
ha
ha
ha
ha
ha
ha
ha
ha
ha!
undefined

Possible duplicate of [Does every Javascript function have to return a value?](https://stackoverflow.com/questions/17337064/does-every-javascript-function-have-to-return-a-value) — Tsvetan Ganev, Jan 26 '18 at 19:39

score 2 · Answer 1 · answered Jan 26 '18 at 19:35

2

laugh doesn't return anything and by default a function will return undefined, and that will pass into your last console.log call.

answered Jan 26 '18 at 19:35

Daniel A. White

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Ele · Answer 2 · 2018-01-26T19:38:44.917

0

Because the function laugh doesn't return any value, so the result is undefined.

Look the modification to return "HELLO", this is just to illustrate.

var laugh = function laughs(y) {
  while (y > 0) {
    console.log("ha");
    y--;
  }

  console.log("ha!");

  return "HELLO";
}

console.log(laugh(10));

edited Jan 26 '18 at 19:38

answered Jan 26 '18 at 19:36

Ele

33,468
7
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@trincot There is any repeat, that code illustrates what I'm answering. Look carefully the `return "HELLO"`. – Ele Jan 26 '18 at 19:39
The modified version is OK now ;-) – trincot Jan 26 '18 at 19:40

Tom O. · Answer 3 · 2018-01-26T19:50:12.597

laugh() does not explicitly return a value; therefore its return type is undefined. You're calling laugh() from within a console.log() - the result being that you see all the console.log() calls that occur within laugh() then, additionally, the undefined being returned by laugh() is being logged to the console.

You could return a string if you want to log the result of the function. Something like this:

var laugh = function laughs(y) {
  var str = '';
  while (y > 0) {
    //console.log("ha");
    str += 'ha\n';
    y--;
  }
  //console.log("ha!");
  str += 'ha!\n';
  return str;
}

console.log(laugh(10));

Alternatively, you could just remove the console.log() enclosing the function call like this:

var laugh = function laughs(y) {
  while (y > 0) {
    console.log("ha");
    y--;
  }
  console.log("ha!");
}

laugh(10);

What my code display this?

3 Answers3