FAQ Topic - How do I convert a Number into a String with exactly 2 decimal places? (2008-10-29)

Discussion in 'Javascript' started by FAQ server, Oct 29, 2008.

  1. FAQ server

    FAQ server Guest

    -----------------------------------------------------------------------
    FAQ Topic - How do I convert a Number into a String with
    exactly 2 decimal places?
    -----------------------------------------------------------------------

    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 the section on "simple decimal arithmetic"
    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 ` Number.prototype.toFixed `, the main problem
    with this is the bugs in JScript's 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 = String(Math.round(X * Number("1e" + N)));
    if (S.search && S.search(/\D/) != -1) {
    return '' + X;
    }
    with (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, Oct 29, 2008
    #1
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  2. In comp.lang.javascript message <4907a788$0$90269$.
    dk>, Wed, 29 Oct 2008 00:00:02, FAQ server <>
    posted:

    And did so in a very timely manner, the topic having been raised in the
    "JavaScript Math vs Excel" thread.

    >FAQ Topic - How do I convert a Number into a String with
    >exactly 2 decimal places?


    > ...


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


    To that line should be appended an indication that the logically-
    following pages should also be read; my current StrU is in the next.
    I'd just append either " ff." or " /ff./", expecting readers to
    understand it. YMMV.

    The functions are the FAQ are NOT what I presently use. My present
    ones, StrU ff. at <URL:http://www.merlyn.demon.co.uk/js-rndg1.htm#GC>
    give the called-for not-too-big numeric fixed-point decimal result when
    possible, and otherwise indicate exactly what the input value was,
    including both Infinities, NaN, null, undefined - and with the correct
    number of spaces, if necessary (the string may be too long, but not too
    short). I was about to assert that they thereby cover all
    possibilities, when I realised that there was one omission - and that I
    could easily fix it.

    I'll let you all think about it for a bit ...

    --
    (c) John Stockton, near London. *@merlyn.demon.co.uk/?.?
    Web <URL:http://www.merlyn.demon.co.uk/> - FAQish topics, acronyms, & links.
    Correct <= 4-line sig. separator as above, a line precisely "-- " (SoRFC1036)
    Do not Mail News to me. Before a reply, quote with ">" or "> " (SoRFC1036)
    Dr J R Stockton, Oct 29, 2008
    #2
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  3. In comp.lang.javascript message <
    rlyn.invalid>, Wed, 29 Oct 2008 20:13:12, Dr J R Stockton
    <> posted:

    >>FAQ Topic - How do I convert a Number into a String with
    >>exactly 2 decimal places?


    >The functions are the FAQ are NOT what I presently use. My present
    >ones, StrU ff. at <URL:http://www.merlyn.demon.co.uk/js-rndg1.htm#GC>
    > ...
    > I was about to assert that they thereby cover all
    >possibilities, when I realised that there was one omission - and that I
    >could easily fix it.
    >
    >I'll let you all think about it for a bit ...


    Over two days have elapsed. Neither the routines in the FAQ, nor any
    others that I had seen (my own included) up to Wednesday evening, can
    represent the difference between +0 and -0.

    The present FAQ routines give a leading space for +0 and -0, and an
    appropriate sign for all other numbers, including infinities and those
    which round to zero.

    To get a signed zero, replace function Sign with
    function Sygn(X) { return X + 1/X > 0 ? "+" : "-" }

    So, in the FAQ, keep Sign (being more commonly wanted?), but give Sygn
    as well.

    The FAQ routines survive missing arguments. They also survive the first
    argument being a Function, Array, or Object. I have been wondering
    whether what they then do can be improved without adding too much code.

    The FAQ is now visible at the URL in FAQ 9.91 :) .

    --
    (c) John Stockton, nr London UK. ?@merlyn.demon.co.uk BP7, Delphi 3 & 2006.
    <URL:http://www.merlyn.demon.co.uk/> TP/BP/Delphi/&c., FAQqy topics & links;
    <URL:http://www.bancoems.com/CompLangPascalDelphiMisc-MiniFAQ.htm> clpdmFAQ;
    NOT <URL:http://support.codegear.com/newsgroups/>: news:borland.* Guidelines
    Dr J R Stockton, Nov 1, 2008
    #3
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