CODEWITHSUNDEEP
javascriptfloating-pointroundingfloor
Hugo G
Hugo G

Reputation: 16494

Fixed number rounding down in JavaScript

Problem

I get numbers from 1 to 5 including all possible floating point numbers in between. The output must contain two digits after comma and in case of after-comma digits they need to be rounded down (floor).

Example input and output:

My Try

My try is doing a Math.floor on the 100x of the number and dividing afterwards to get rid of the unwanted digits after comma. The Number.toFixed(2) gets me the possibly missing zeros afterwards:

(Math.floor(input * 100) / 100).toFixed(2)

The problem with this is JavaScript's floating point inprecision:

Math.floor(4.14 * 100) / 100
// results in 4.13 because 4.14 * 100 is 413.99999999999994

Upvotes: 1

Views: 1686

Answers (1)

Silviu Burcea
Silviu Burcea

Reputation: 5348

function formatNumber(x) {
  // convert it to a string
  var s = "" + x;
  // if x is integer, the point is missing, so add it
  if (s.indexOf(".") == -1) {
    s += ".";
  }
 // make sure if we have at least 2 decimals
  s += "00";
  // get the first 2 decimals
  return s.substring(0, s.indexOf(".") + 3);
}

document.write(1 + " -> " + formatNumber(1) + "<br/>");
document.write(4.3 + " -> " + formatNumber(4.3) + "<br/>");
document.write(1.1000 + " -> " + formatNumber(1.1000) + "<br/>");
document.write(1.5999 + " -> " + formatNumber(1.5999) + "<br/>");
document.write(4.14 + " -> " + formatNumber(4.14) + "<br/>");

Here is my attempt, the idea is documented in the code. Of course, there are probably better solutions, but this is a quick & dirty solution.

Upvotes: 2

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