Multiplying individual digits in a number with each other in JavaScript

Question

I'm trying to make a program that will take the digits in a number and multiply them with each other. So 583 would be 5*8*3 = 120.

Its not working as intended, its just returning the number that was put in.

How can I fix it?

Here's the code:

function persistence(num) {
  //code me
  numString = num.toString();
  numArray = numString.split().map(function(t) {
    return parseInt(t)
  });


  function reducer(theNumArray) {
    let sum = 1;
    for (var i = 0; i < theNumArray.length; i++) {
      sum = sum * theNumArray[i];

    }
    return sum;
  }
  newNum = reducer(numArray);

  console.log(newNum);
};

persistence(485);

[What does your step debugger tell you?](http://stackoverflow.com/questions/25385173/what-is-a-debugger-and-how-can-it-help-me-diagnose-problems) — , Apr 09 '18 at 18:01
Possible duplicate of [What is a debugger and how can it help me diagnose problems?](https://stackoverflow.com/questions/25385173/what-is-a-debugger-and-how-can-it-help-me-diagnose-problems) — , Apr 09 '18 at 18:02

Nina Scholz · Answer 1 · 2018-04-09T18:03:47.003

You could split the string with an empty string, for getting single digits. Then covert, if required all strings to a number.

function reducer(theNumArray) {
    var i, sum = 1;
    for (i = 0; i < theNumArray.length; i++) {
        sum *= theNumArray[i];
    }
    return sum;
}

function persistence(num) {
    var numArray = num.toString().split('').map(Number);
    return reducer(numArray);
}

console.log(persistence(485));

A shorter approach could be just taking the single digits by using a spread syntax with an iterator for strings, then just multiply the values and return the result.

function persistence(number) {
    return [...number.toString()].reduce((p, v) => p * v);
}

console.log(persistence(485));

really clean solution with reduce. – Hunter McMillen Apr 09 '18 at 17:58 — Hunter McMillen, Apr 09 '18 at 17:58

Narendra Jadhav · Answer 2 · 2018-04-09T18:15:37.553

You just need to change inside split('')

DEMO

function persistence(num) {
  //code me
  numString = num.toString();
  numArray = numString.split('').map(function(t) {
    return parseInt(t)
  });

  function reducer(theNumArray) {
    let sum = 1;
    for (var i = 0; i < theNumArray.length; i++) {
      sum = sum * theNumArray[i];

    }
    return sum;
  }
  newNum = reducer(numArray);

  console.log(newNum);
};

persistence(485);

.as-console-wrapper { max-height: 100% !important; top: 0; }

You can also use reduce method for array.

ES5

function persistence(num) {
  let result = num.toString().split('').reduce(function(total, v) {
    return total * v
  }, 1);
  console.log(result);
};

persistence(485);

.as-console-wrapper { max-height: 100% !important; top: 0; }

ES6

It Can be more easy with Spread_syntax of ES6.

function persistence(num) {
  let result = [...num.toString()].reduce((total, v) => total * v, 1);
  console.log(result);
};

persistence(485);

.as-console-wrapper { max-height: 100% !important; top: 0; }

Scath · Answer 3 · 2018-04-09T18:04:27.507

You don't need to split the string you can just reference the chars by their number. This seems to work fine example for 4*8*5= 160.

The other way (introduced in ECMAScript 5) is to treat the string as an array-like object, where individual characters correspond to a numerical index

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String

function persistence(num) {
  numString = num.toString();
  let sum = 1;
  for (var i = 0; i < numString.length; i++) {
    sum = sum * numString[i];
  }
  console.log(sum);
};
persistence(485);

Mike James · Answer 4 · 2018-04-09T18:10:40.420

1

Assuming num is a positive integer:

    function persistence(num) {
    var ans=1;    
    while( num!==0){
            ans=ans*(num-Math.floor(num/10)*10);
            num=Math.floor(num/10);

        }
        console.log(ans);
    }

    persistence(123);

This is based on (num-Math.floor(num/10)*10) extracting the least significant digit. For example

123 - Math.floor(123/10)*10

123 - 12*10

123 - 120

3

And so on after reducing num by one digits by integer divide by 10. You don't need strings.

edited Apr 09 '18 at 18:10

answered Apr 09 '18 at 18:05

Mike James

749
6
9

`num-Math.floor(num/10)*10` could be just `num % 10` – georg Apr 09 '18 at 18:16

score 1 · Answer 5 · answered Apr 09 '18 at 18:10

according to this the split method will have different results based on the inputs (obvious right?):

No Separator-> If you don't pass a separator argument to the split method, the resulting array will have a single element consisting of the entire string

so, basically from here:

numString.split()

you will get an array with the string (your number) inside of it, this should be changed to:

numString.split('')

so your whole code should be like this:

 function persistence(num) {
    numString = num.toString();
    numArray = numString.split().map(function(t) {
       return parseInt(t)
    });


 function reducer(theNumArray) {
     let sum = 1;
     for (var i = 0; i < theNumArray.length; i++) {
         sum = sum * theNumArray[i];
     }
     return sum;
 }
 newNum = reducer(numArray);

 console.log(newNum);
};

persistence(485);

Multiplying individual digits in a number with each other in JavaScript

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