When the result is round (1.10 1.30) does not display the 2nd decimal How do I do it?

Question

My program (which uses Math.round) does not display the second decimal when the result is round (ex: 1.10, 1.30) while yes when the result is not round (ex: 1.24, 2.47). How to change this?

function calcAmount2() {
  var userAmount2 = document.getElementById("amount2").value;
  if (userAmount2 = Number(amount2.value)) {
    document.getElementById("marginAmount2").textContent =
      Math.round(userAmount2 * 3) / 100 + "€";
  }
}

(expected)1.10, 1.30 instead of (actually) 1.1 1.3

JavaScript does not have significant places. You can use toFixed()... too lazy to find the dupe — epascarello, Apr 29 '19 at 14:14
Possible duplicate of [Formatting a number with exactly two decimals in JavaScript](https://stackoverflow.com/questions/1726630/formatting-a-number-with-exactly-two-decimals-in-javascript) — Dexygen, Apr 29 '19 at 14:15

JensW · Answer 1 · 2019-04-29T14:18:14.903

4

(Math.round(userAmount2 * 3) / 100).toFixed(2) + "€";

toFixed sets the number to always have 2 decimals.

edited Apr 29 '19 at 14:18

answered Apr 29 '19 at 14:14

JensW

442
2
12

Please don't post code-only answers. Explain your answer and add relevant references. – Daniel W. Apr 29 '19 at 14:16
Bravo JensW! Simple and efficient. You are a best. – Philippe Delestan Apr 29 '19 at 14:28

score 2 · Answer 2 · answered Apr 29 '19 at 14:14

2

I believe this is a duplicate of Format number to always show 2 decimal places

You want to use .toFixed(2) it seems, though be aware the result will be a String.

answered Apr 29 '19 at 14:14

pmiller3

161
5

Yes! pmiller3. Short and precise, if my english is good. You are a "one" guy. – Philippe Delestan Apr 29 '19 at 14:30
Thank you @PhilippeDelestan! Be sure to upvote and choose an answer as well - all three here seem worthwhile. – pmiller3 Apr 29 '19 at 14:39

wentjun · Answer 3 · 2019-04-29T14:27:59.250

1

I am not sure how specific your answer has to be, but I would recommend you to use this instead:

const res = Number(Math.round(userAmount2 +'e2')+'e-2');

This is because toFixed has the rounding problem for some values such as 21.005.

Let me prove it to you over here:

    
console.log(Number(Math.round(20.005 +'e2')+'e-2'));
console.log(20.005.toFixed(2));

edited Apr 29 '19 at 14:27

answered Apr 29 '19 at 14:18

wentjun

40,384
10
95
107

You're right, Gojun! There is problem of rounded value with 3 decimals. But, we can see as cool with euro, sometimes only. So, i willtest youre solution but i'm not understand this code. what is signification of "e2" and e-2"? I'm a beginner in javascript and i prefere when i understand what i doThanks a lot. – Philippe Delestan Apr 29 '19 at 18:27
@PhilippeDelestan ah, I must have missed out that part on `e`. e in scientific/numeric notation refers to the number, times 10 to the power of the suffix! Therefore, `e2` means x10^2, and `e-2` means x10^-2. – wentjun Apr 29 '19 at 19:05
I am essentially 'scaling' the number by two figures (x100) across the decimal point, rounding the value, followed by multiplying it back by (10^-2), in order to avoid all that floating point issues. – wentjun Apr 29 '19 at 19:10
Yes, i understand very well. Thank you, Gojun. – Philippe Delestan Apr 29 '19 at 20:10

When the result is round (1.10 1.30) does not display the 2nd decimal How do I do it?

3 Answers3