Javascript Round Number function

28. Feb, 2008 3 Comments

function round_number(n, d) {
  n = n - 0;
  if (d == null) d = 2;
  var f = Math.pow(10, d);
  n += Math.pow(10, - (d + 1));
  n = Math.round(n * f) / f;
  n += Math.pow(10, - (d + 1));
  n += '';
  return d == 0 ? n.substring(0, n.indexOf('.')) :  n.substring(0, n.indexOf('.') + d + 1);
}

Example:

price = round_number(4174.315);
alert(price); //Result: 4174.32

Author: insic

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3 Responses to “Javascript Round Number function”

Brian McAllister Reply 12. Aug, 2008 at 2:45 pm

why not use the toFixed method? It also rounds the result i.e.

var number = 3.14567
alert(number.toFixed(2));

==> 3.15
insic_19 Reply 13. Aug, 2008 at 4:39 am

that is a nice idea also. thanks for the tip brian.
ger Reply 05. May, 2009 at 4:29 am

Actualy there are many cases when we do not want pure math round for prices, as
1st: prices should be always rounded up (e.g. $4.021 => $4.05)
2nd: usually round to 5 cents (unless you have those stuppid 9.99 prices)

So, we get wierd price like $4.3126 after some calculation (item price + some delivery + WAT * % discount bla-bla-bla) and need to get nice-looking price like $4.35

function roundPrice(price)
{
var priceMultiplied = Math.ceil(price*100);
var reminder = priceMultiplied % 5;
var compliment = reminder?5-reminder:0;
var priceRounded = (priceMultiplied + compliment)/100;
return priceRounded.toFixed(2);
}

test cases:
roundPrice(18.32)   = 18.35
roundPrice(20.01)   = 20.05
roundPrice(21.39) = 21.40
roundPrice(29.95)   = 29.95
roundPrice(29.96) = 30.00
roundPrice(29.951) = 30.00