Get Number of Decimal Places with Javascript

Question

How would I calculate the number of decimal places (not digits) of a real number with Javascript?

function countDecimals(number) {

}

For example, given 245.395, it should return 3.

Answer 1

Like this:

var val = 37.435345;
var countDecimals = function(value) {
  let text = value.toString()
  // verify if number 0.000005 is represented as "5e-6"
  if (text.indexOf('e-') > -1) {
    let [base, trail] = text.split('e-');
    let deg = parseInt(trail, 10);
    return deg;
  }
  // count decimals for number in representation like "0.123456"
  if (Math.floor(value) !== value) {
    return value.toString().split(".")[1].length || 0;
  }
  return 0;
}
countDecimals(val);

Answer 2

The main idea is to convert a number to string and get the index of "."

var x = 13.251256;
var text = x.toString();
var index = text.indexOf(".");
alert(text.length - index - 1);

Answer 3

Here is a method that does not rely on converting anything to string:

function getDecimalPlaces(x,watchdog)
{
    x = Math.abs(x);
    watchdog = watchdog || 20;
    var i = 0;
    while (x % 1 > 0 && i < watchdog)
    {
        i++;
        x = x*10;
    }
    return i;
}

Note that the count will not go beyond watchdog value (defaults to 20).

Answer 4

I tried some of the solutions in this thread but I have decided to build on them as I encountered some limitations. The version below can handle: string, double and whole integer input, it also ignores any insignificant zeros as was required for my application. Therefore 0.010000 would be counted as 2 decimal places. This is limited to 15 decimal places.

  function countDecimals(decimal)
    {
    var num = parseFloat(decimal); // First convert to number to check if whole

    if(Number.isInteger(num) === true)
      {
      return 0;
      }

    var text = num.toString(); // Convert back to string and check for "1e-8" numbers
    
    if(text.indexOf('e-') > -1)
      {
      var [base, trail] = text.split('e-');
      var deg = parseInt(trail, 10);
      return deg;
      }
    else
      {
      var index = text.indexOf(".");
      return text.length - index - 1; // Otherwise use simple string function to count
      }
    }

Answer 5

You can use a simple function that splits on the decimal place (if there is one) and counts the digits after that. Since the decimal place can be represented by '.' or ',' (or maybe some other character), you can test for that and use the appropriate one:

function countPlaces(num) {
    var sep = String(23.32).match(/\D/)[0];
    var b = String(num).split(sep);
  return b[1]? b[1].length : 0;
}

console.log(countPlaces(2.343)); // 3
console.log(countPlaces(2.3));   // 1
console.log(countPlaces(343.0)); // 0
console.log(countPlaces(343));   // 0

Answer 6

Based on Gosha_Fighten's solution, for compatibility with integers:

function countPlaces(num) {
    var text = num.toString();
    var index = text.indexOf(".");
    return index == -1 ? 0 : (text.length - index - 1);
}

Answer 7

based on LePatay's solution, also take care of the Scientific notation (ex: 3.7e-7) and with es6 syntax:

function countDecimals(num) {
  let text = num.toString()
  if (text.indexOf('e-') > -1) {
    let [base, trail] = text.split('e-')
    let elen = parseInt(trail, 10)
    let idx = base.indexOf(".")
    return idx == -1 ? 0 + elen : (base.length - idx - 1) + elen
  }
  let index = text.indexOf(".")
  return index == -1 ? 0 : (text.length - index - 1)
}

Answer 8

var value = 888;
var valueLength = value.toString().length;