Functions are not called from recursive functions in JavaScript

Question

function and(arr) {
  if (arr.length === 0) {
    return true;
  }

  const head = arr[0];
  const tail = arr.slice(1);

  return head && and(tail);
}

and([true, true, false]);

I have this recursion called 4 times and at the end

if (arr.length === 0) {
    return true;
  }

I thought it would end with

However, the function has only been called 3 times !!

head: [true]    tail: [true,false]
head: [true]    tail: [false]
head: [false]   tail: []

This is the result I checked

  if (arr.length === 0) {
    return true;
  }

This condition didn't even work.

I need help.

Sorry for using the translator

@cybercoder Then the function would be guaranteed to return true, which goes against the whole point of the function. — Aplet123
– Aplet123, Commented Nov 22, 2020 at 12:14
@Aplet123 the question is about count of calling happens in recursion! So he/she have to change the body of function to achieve correct answer. I made a comment to guide not an answer! — Vahid Alimohamadi
– Vahid Alimohamadi, Commented Nov 22, 2020 at 13:49

Aplet123 · Accepted Answer · 2020-11-22 12:05:33Z

5

In Javascript and many other languages, && is short-circuiting. This means that if you have a && f(), and a is false, the condition is already known to be false, so f is never ran. Since the head of your array is false in the third call, the && operator will short-circuit and return false without even continuing the recursion. If you try and([true, true, true]) you will notice that it does go all the way to a 0-length array and your condition will do something.

answered Nov 22, 2020 at 12:05

Aplet123

35.8k1 gold badge41 silver badges66 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

Functions are not called from recursive functions in JavaScript

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related