Is there a reliable way in JavaScript to obtain the number of decimal places of an arbitrary number?

Question

It\'s important to note that I\'m not looking for a rounding function. I am looking for a function that returns the number of decimal places in an arbitrary number\'s simpli

Answer 1

Well, I use a solution based on the fact that if you multiply a floating-point number by the right power of 10, you get an integer.

For instance, if you multiply 3.14 * 10 ^ 2, you get 314 (an integer). The exponent represents then the number of decimals the floating-point number has.

So, I thought that if I gradually multiply a floating-point by increasing powers of 10, you eventually arrive to the solution.

let decimalPlaces = function () {
   function isInt(n) {
      return typeof n === 'number' && 
             parseFloat(n) == parseInt(n, 10) && !isNaN(n);
   }
   return function (n) {
      const a = Math.abs(n);
      let c = a, count = 1;
      while (!isInt(c) && isFinite(c)) {
         c = a * Math.pow(10, count++);
      }
      return count - 1;
   };
}();

for (const x of [
  0.0028, 0.0029, 0.0408,
  0, 1.0, 1.00, 0.123, 1e-3,
  3.14, 2.e-3, 2.e-14, -3.14e-21,
  5555.0, 5555, 555.5, 555.50, 0.0000005, 5e-7, 0.00000055, 5e-8,
  0.000006, 0.0000007,
  0.123, 0.121, 0.1215
]) console.log(x, '->', decimalPlaces(x));