# FAQ Topic - How do I convert a Number into a String with exactly 2 decimal places? (2008-08-18)

Discussion in 'Javascript' started by FAQ server, Aug 18, 2008.

1. ### FAQ serverGuest

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FAQ Topic - How do I convert a Number into a String with
exactly 2 decimal places?
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When formatting money for example, to format 6.57634 to
6.58, 6.5 to 6.50, and 6 to 6.00?

Rounding of x.xx5 is uncertain, as such numbers are not
represented exactly. See section 4.7 for Rounding issues.

N = Math.round(N*100)/100 only converts N to a Number of value
close to a multiple of 0.01; but document.write(N) does not give
trailing zeroes.

ECMAScript Ed. 3.0 (JScript 5.5 [but buggy] and JavaScript 1.5)
introduced N.toFixed, the main problem with this is the bugs in
JScripts implementation.

Most implementations fail with certain numbers, for example 0.07.
The following works successfully for M>0, N>0:

function Stretch(Q, L, c) { var S = Q
if (c.length>0) while (S.length<L) { S = c+S }
return S
}
function StrU(X, M, N) { // X>=0.0
var T, S=new String(Math.round(X*Number("1e"+N)))
if (S.search && S.search(/\D/)!=-1) { return ''+X }
with (new String(Stretch(S, M+N, '0')))
return substring(0, T=(length-N)) + '.' + substring(T)
}
function Sign(X) { return X>0 ? "+" : X<0 ? "-" : " " }
function StrS(X, M, N) { return Sign(X)+StrU(Math.abs(X), M, N) }
Number.prototype.toFixed = function(n){ return StrS(this,1,n) };

http://www.merlyn.demon.co.uk/js-round.htm

http://msdn2.microsoft.com/en-us/library/sstyff0z.aspx

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FAQ server, Aug 18, 2008

2. ### Dr J R StocktonGuest

In comp.lang.javascript message <48a8ad77\$0\$90272\$.
dk>, Sun, 17 Aug 2008 23:00:02, FAQ server <>
posted:

S is String.

> if (S.search && S.search(/\D/)!=-1) { return ''+X }

if (/\D/.test(S)) return SpcsTo(X, M+N+1)

Is there any likelihood, nowadays, that in either of the above lines the
method (search or test) will not exist as expected?

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Dr J R Stockton, Aug 19, 2008