How to round a number with multiple decimal places. Javascript

Question

I am trying to create a function that can take a number and the number of decimal places and round the number to the exact decimal places that are going to be given. I am using parseInt(prompt()) in order to gave the number and the number of decimal places.

For example,

round(3.141519, 2) -> 3.14
round(5986.32456, 4) -> 5986.3246

Can someone help me with this?

Google: [site:stackoverflow.com javascript round to decimal](https://www.google.com/search?q=site%3Astackoverflow.com+javascript+round+to+decimal) — , Dec 20 '16 at 19:24
Can't you use Math.round? https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/Math/round — Hosar, Dec 20 '16 at 19:25
Possible duplicate of [JavaScript math, round to two decimal places](http://stackoverflow.com/questions/15762768/javascript-math-round-to-two-decimal-places) — Heretic Monkey, Dec 20 '16 at 19:25
Possible duplicate of [Formatting a number with exactly two decimals in JavaScript](http://stackoverflow.com/questions/1726630/formatting-a-number-with-exactly-two-decimals-in-javascript) — Ninja, Dec 20 '16 at 19:26

score 2 · Answer 1 · answered Dec 20 '16 at 19:23

2

You can use toFixed

check the following

 console.log(3.141519.toFixed(2))
 console.log(5986.32456.toFixed(4))

answered Dec 20 '16 at 19:23

Geeky

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Note, `toFixed` returns a string. – Carcigenicate Dec 20 '16 at 19:29

Rob M. · Accepted Answer · 2016-12-20T22:03:06.273

1

Here is a short function that will allow you to specify the precision and returns a number:

function round(number, places) {
   number = parseFloat(number, 10);
   var e  = parseInt(places || 2, 10);
   var m = Math.pow(10, e);
   return Math.floor(number * m) / m;
}

Or a slightly shorter ES6 function:

const round = (number, places=2) => {
   const m = Math.pow(10, places);
   return Math.floor(number * m) / m;
}

edited Dec 20 '16 at 22:03

answered Dec 20 '16 at 19:30

Rob M.

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I used the first solution, and when i run the function it gives me NaN. – Leo Dec 20 '16 at 21:55
Shouldn't it print out the rounded number with as many decimal places that i want? – Leo Dec 20 '16 at 21:57
@Leo Are you not passing it numbers? `round(3.1456, 3)` works for me... – Rob M. Dec 20 '16 at 21:59
I updated my first solution to use `parseFloat` and `parseInt` in case you pass it strings – Rob M. Dec 20 '16 at 22:03
I guess i am doing something wrong with my solution.. I can't figure out what. – Leo Dec 20 '16 at 22:05
function round(number, places) { var number = parseInt(prompt("Please enter number:")); var places = parseInt(prompt("Please enter number of decimal places:")); var e = places || 2; var m = Math.pow(10, e); return Math.floor(number * m) / m; } document.write(round()); Where is my mistake? Can you tell me? – Leo Dec 20 '16 at 22:11
Yeah, you are using `parseInt` on the "Please enter a number", that needs to be `parseFloat`. You could also remove the `number` and `places` arguments from the function declaration since you are getting that data using `prompt` – Rob M. Dec 20 '16 at 22:17
Thanks! You ROCK! :D – Leo Dec 20 '16 at 22:18
Glad to help, Leo! :D – Rob M. Dec 20 '16 at 22:18

How to round a number with multiple decimal places. Javascript

2 Answers2