CODEWITHSUNDEEP
javascript
Peter
Peter

Reputation: 4701

Calculating modulos using JavaScript returns undefined

I wrote a function to calculate the modulus of a function but when I run it in the console it always returns undefined. If I use the console.log I can see that it is calculating the correct value.

function modulo(sum, divider){ 
  function loop(difference){ 
    if(difference < divider){ 
     console.log(difference)
     return difference
    } else { 
       setTimeout(loop(difference - divider), 0)
    } 
  } 
  
  return loop(sum - divider) 
}

modulo(8, 5) // 3

what I want is this to return the answer e.g.

var result = modulo(8, 5) // 3

Update:

A better solution to this problem would be

modulo = function (x,y){ return x - y * Math.floor(x/y) }

Upvotes: 0

Views: 483

Answers (3)

simonzack
simonzack

Reputation: 20928

To answer your original question, setTimeout is asynchronous, and your loop function returns undefined, hence you get undefined. To make it do what you want, call loop directly, or use promises.

But on the other hand, even if you were to implement modulus, this is a poor approach. Use some better division algorithms instead.

Upvotes: 2

cychoi
cychoi

Reputation: 3090

Because your code does not return value from the loop.

Try this:

function modulo(sum, divider) {
  function loop(difference) {
    if (difference < divider) {
      return difference;
    } else {
      return loop(difference - divider);
    }
  }

  return loop(sum - divider);
}

alert(modulo(8, 5));

Upvotes: 0

James Donnelly
James Donnelly

Reputation: 128791

You don't need to create a new function for this, JavaScript already has it's own modulus operator: %.

8 % 5
-> 3

If you really want to turn this into a function, you can simply:

function modulo(sum, divider) {
    return sum % divider;
}

modulo(8, 5);
-> 3

Upvotes: 3

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