Rounding-off from whole numbers to whole numbers in JavaScript?

user_17497178 0
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So I have some numbers x = 320232 y = 2301 z = 12020305. I want to round these numbers off using JavaScript so that they become x = 320000 y = 2300 z = 12000000.

I tried Math.round and Math.floor but turns out that they only work with decimal values like a = 3.1; Math.round(a); // Outputs 3 and not whole numbers.

So my question is can we round of whole numbers using JavaScript and If yes then how?

Edit: I want it to the round of to the starting 3 digit places as seen in the variables above. Like If there was another variable called c = 423841 It should round off to become c = 424000.

math javascript
3 Answers

You could work with the logarithm of ten and adjust the digits.

const
    format = n => v => {
        if (!v) return 0;
        const l = Math.floor(Math.log10(Math.abs(v))) - n + 1;

        return Math.round(v / 10 ** l) * 10 ** l;
    };

console.log([0, -9876, 320232, 2301, 12020305, 123456789].map(format(3)));

user_14476750

The solution is to first calculate how many numbers need to be rounded away, and then use that in a round.

Math.round(1234/100)*100 would round to 1200 so we can use this to round. We then only need to determan what to replace 100 with in this example.

That is that would be a 1 followed by LENGTH - 3 zeros. That number can be calculated as it is 10 to the power of LENGTH - 3, in JS: 10 ** (length - 3).

var x = 320232;
var y = 2301;
var z = 12020305;

function my_round(number){
  var org_number = number;
  
  // calculate integer number
  var count = 0;
  if (number >= 1) ++count;

  while (number / 10 >= 1) {
    number /= 10;
    ++count;
  }
  
  // length - 3
  count = Math.round(count) - 3;
  if (count < 0){
    count = 0;
  }
  
  // 10 to the power of (length - 3)
  var helper = 10 ** count;
  
  return Math.round(org_number/helper)*helper;
}

alert(my_round(x));
alert(my_round(y));
alert(my_round(z));

It is not the prettiest code, though I tried to make it explainable code.

user_56006520

This should work:

function roundToNthPlace(input, n) {
    let powerOfTen = 10 ** n
    return Math.round(input/powerOfTen) * powerOfTen;
}

console.log([320232, 2301,12020305, 423841].map(input => roundToNthPlace(input, 3)));

Output: [320000, 2000, 12020000, 424000]
user_34197260
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