Why this javascript code give me Nan in the last line of output? I need the reason please

Question

x = 4;
console.log(x);
var x = 10,
  y = 2;

function z(x) {
  while (x > 0) {
    if (x > 0) {
      break;
    } else {
      x = x - y;
      return z(x);
    }
    return x;
  }
}
console.log(x);
console.log(z(x) + z(x + y));

I need explain for the output of the last line?, where the output is NaN.

When you break out of the loop, you don't `return x;`, since that's inside the loop. Maybe you meant to put that one line down? Or change `break` to `return x`. — Barmar, Aug 12 '20 at 15:27
The code doesn't really make sense. You only go into the loop body when `x > 0`, so the `if` condition will always be true. — Barmar, Aug 12 '20 at 15:29
@Barmar I totally mean this code, thank you for the clarity ❤ — The Hopeful, Aug 12 '20 at 15:30
z(n) is always undefined. Adding an undefined entity to any other entity gives `NaN`. Refer [this](https://stackoverflow.com/questions/49550626/why-is-null-1-1-but-undefined-1-nan) for the explanation. — Kunal Kukreja, Aug 12 '20 at 15:31

score 1 · Answer 1 · answered Aug 12 '20 at 15:33

1

Because z(x) and z(x + y) are returning undefined.

answered Aug 12 '20 at 15:33

Pritom K. Paul

11
1

score 1 · Answer 2 · answered Aug 12 '20 at 15:35

It is returning NaN because when you call...

console.log(z(x)+z(x+y));

not all paths within the function return anything. In fact, in the if block it just breaks and nothing is ever returned.

        if(x>0){
           break;
        }

If x == 10 then the while loop will just break and nothing is returned. You can fix this by switching out the break; for return x; which is ultimately doing the same thing but not returning NaN.

        if(x>0){
           return x;
        }

score 0 · Answer 3 · answered Aug 12 '20 at 15:29

0

function z(x) {
  while (x > 0) {
    if (x > 0) {
      break;
    } else {
      x = x - y;
      return z(x);
    }
    return x;
  }
}

For this function, think about the case of x === 10. The while condition is true, so we enter that. Next. We get to the if (x > 0), which is true, so the break; statement is hit. This breaks out of the while loop, and we exit the function with no return value. Thus, z(x) returns undefined.

z(x + y) similarly returns undefined if you follow the same logic.

undefined + undefined === NaN

answered Aug 12 '20 at 15:29

Jacob

77,566
24
149
228

The `while` condition is `x > 0`, so that if/else statement is pointless. The while loop already checks the condition on each iteration. Perhaps you should explain what you want the function to do so we can weigh in on what should be modified. – Jacob Aug 12 '20 at 15:42
Modify condition if(x > 0) to if (x <= 2) – The Hopeful Aug 12 '20 at 15:45

score 0 · Answer 4 · answered Aug 12 '20 at 15:32

whatever you want to be done, you function does not return anything by itself. Just add return:

function z(x) {
  display.log(x, y)
  while (x > 0) {
    if (x > 0) {
      break;
    } else {
      x = x - y;
      return z(x);
    }
    return x;
  }
  return x /// this is what was added
}

score 0 · Answer 5 · answered Aug 12 '20 at 15:34

0

It happens because hits break when x > 0:

 if (x > 0) {
  break;

answered Aug 12 '20 at 15:34

FBlade

361
1
8

score 0 · Accepted Answer · answered Aug 12 '20 at 15:43

0

function z() is always returning undefined. So :

z(x) & z(x+y) are undefined

Javascript addition on undefined values returns NaN. So

z(x) + z(x+y) is NaN

answered Aug 12 '20 at 15:43

ankur1812

97
4

Why this javascript code give me Nan in the last line of output? I need the reason please

6 Answers6