下面是Patrick Desjardins（别名Daok）代码，添加了一些注释和一些小改动：

/*
decimal_sep: character used as decimal separator, it defaults to '.' when omitted
thousands_sep: char used as thousands separator, it defaults to ',' when omitted
*/
Number.prototype.toMoney = function(decimals, decimal_sep, thousands_sep)
{
   var n = this,
   c = isNaN(decimals) ? 2 : Math.abs(decimals), // If decimal is zero we must take it. It means the user does not want to show any decimal
   d = decimal_sep || '.', // If no decimal separator is passed, we use the dot as default decimal separator (we MUST use a decimal separator)

   /*
   According to [https://stackoverflow.com/questions/411352/how-best-to-determine-if-an-argument-is-not-sent-to-the-javascript-function]
   the fastest way to check for not defined parameter is to use typeof value === 'undefined'
   rather than doing value === undefined.
   */
   t = (typeof thousands_sep === 'undefined') ? ',' : thousands_sep, // If you don't want to use a thousands separator you can pass empty string as thousands_sep value

   sign = (n < 0) ? '-' : '',

   // Extracting the absolute value of the integer part of the number and converting to string
   i = parseInt(n = Math.abs(n).toFixed(c)) + '',

   j = ((j = i.length) > 3) ? j % 3 : 0;
   return sign + (j ? i.substr(0, j) + t : '') + i.substr(j).replace(/(\d{3})(?=\d)/g, "$1" + t) + (c ? d + Math.abs(n - i).toFixed(c).slice(2) : '');
}

这里有一些测试：

// Some tests (do not forget parenthesis when using negative numbers and number with no decimals)
alert(123456789.67392.toMoney() + '\n' + 123456789.67392.toMoney(3) + '\n' + 123456789.67392.toMoney(0) + '\n' + (123456).toMoney() + '\n' + (123456).toMoney(0) + '\n' + 89.67392.toMoney() + '\n' + (89).toMoney());

// Some tests (do not forget parenthesis when using negative numbers and number with no decimals)
alert((-123456789.67392).toMoney() + '\n' + (-123456789.67392).toMoney(-3));

次要变化包括：

移动了一点Math.abs（小数），只有当不是NaN时才能执行。decimal_sep不能再是空字符串（必须使用某种十进制分隔符）我们使用typeof thousand_sep===“undefined”，如How best to determine if a argument is not send to JavaScript function中所建议的不需要（+n||0），因为这是Number对象

JSFiddle公司

function CurrencyFormatted(amount)
{
    var i = parseFloat(amount);
    if(isNaN(i)) { i = 0.00; }
    var minus = '';
    if(i < 0) { minus = '-'; }
    i = Math.abs(i);
    i = parseInt((i + .005) * 100);
    i = i / 100;
    s = new String(i);
    if(s.indexOf('.') < 0) { s += '.00'; }
    if(s.indexOf('.') == (s.length - 2)) { s += '0'; }
    s = minus + s;
    return s;
}

来自WillMaster。

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/NumberFormat示例：使用区域设置

此示例显示了本地化数字格式的一些变体。为了获得应用程序用户界面中使用的语言的格式，请确保使用locales参数指定该语言（可能还有一些回退语言）：

变量编号=12346.789；//德语使用逗号作为小数分隔符，句点表示千console.log（新Intl.NumberFormat（'de-de'）.format（数字））；//→123.456,789//大多数阿拉伯语国家的阿拉伯语使用真正的阿拉伯数字console.log（新Intl.NumberFormat（'ar-EG'）.format（数字））；//→١٢٣٤٥٦٫٧٨٩//印度使用数千/十万/千个分隔符console.log（新Intl.NumberFormat（'en-IN'）.format（数字））；

PHP函数“number_format”有一个JavaScript端口。

我发现它非常有用，因为它易于使用，并且对PHP开发人员来说是可识别的。

function number_format (number, decimals, dec_point, thousands_sep) {
    var n = number, prec = decimals;

    var toFixedFix = function (n,prec) {
        var k = Math.pow(10,prec);
        return (Math.round(n*k)/k).toString();
    };

    n = !isFinite(+n) ? 0 : +n;
    prec = !isFinite(+prec) ? 0 : Math.abs(prec);
    var sep = (typeof thousands_sep === 'undefined') ? ',' : thousands_sep;
    var dec = (typeof dec_point === 'undefined') ? '.' : dec_point;

    var s = (prec > 0) ? toFixedFix(n, prec) : toFixedFix(Math.round(n), prec);
    // Fix for Internet Explorer parseFloat(0.55).toFixed(0) = 0;

    var abs = toFixedFix(Math.abs(n), prec);
    var _, i;

    if (abs >= 1000) {
        _ = abs.split(/\D/);
        i = _[0].length % 3 || 3;

        _[0] = s.slice(0,i + (n < 0)) +
               _[0].slice(i).replace(/(\d{3})/g, sep+'$1');
        s = _.join(dec);
    } else {
        s = s.replace('.', dec);
    }

    var decPos = s.indexOf(dec);
    if (prec >= 1 && decPos !== -1 && (s.length-decPos-1) < prec) {
        s += new Array(prec-(s.length-decPos-1)).join(0)+'0';
    }
    else if (prec >= 1 && decPos === -1) {
        s += dec+new Array(prec).join(0)+'0';
    }
    return s;
}

（原文注释栏，包括以下示例和到期信用）

// Formats a number with grouped thousands
//
// version: 906.1806
// discuss at: http://phpjs.org/functions/number_format
// +   original by: Jonas Raoni Soares Silva (http://www.jsfromhell.com)
// +   improved by: Kevin van Zonneveld (http://kevin.vanzonneveld.net)
// +     bugfix by: Michael White (http://getsprink.com)
// +     bugfix by: Benjamin Lupton
// +     bugfix by: Allan Jensen (http://www.winternet.no)
// +    revised by: Jonas Raoni Soares Silva (http://www.jsfromhell.com)
// +     bugfix by: Howard Yeend
// +    revised by: Luke Smith (http://lucassmith.name)
// +     bugfix by: Diogo Resende
// +     bugfix by: Rival
// +     input by: Kheang Hok Chin (http://www.distantia.ca/)
// +     improved by: davook
// +     improved by: Brett Zamir (http://brett-zamir.me)
// +     input by: Jay Klehr
// +     improved by: Brett Zamir (http://brett-zamir.me)
// +     input by: Amir Habibi (http://www.residence-mixte.com/)
// +     bugfix by: Brett Zamir (http://brett-zamir.me)
// *     example 1: number_format(1234.56);
// *     returns 1: '1,235'
// *     example 2: number_format(1234.56, 2, ',', ' ');
// *     returns 2: '1 234,56'
// *     example 3: number_format(1234.5678, 2, '.', '');
// *     returns 3: '1234.57'
// *     example 4: number_format(67, 2, ',', '.');
// *     returns 4: '67,00'
// *     example 5: number_format(1000);
// *     returns 5: '1,000'
// *     example 6: number_format(67.311, 2);
// *     returns 6: '67.31'
// *     example 7: number_format(1000.55, 1);
// *     returns 7: '1,000.6'
// *     example 8: number_format(67000, 5, ',', '.');
// *     returns 8: '67.000,00000'
// *     example 9: number_format(0.9, 0);
// *     returns 9: '1'
// *     example 10: number_format('1.20', 2);
// *     returns 10: '1.20'
// *     example 11: number_format('1.20', 4);
// *     returns 11: '1.2000'
// *     example 12: number_format('1.2000', 3);
// *     returns 12: '1.200'

http://code.google.com/p/javascript-number-formatter/:

短、快、灵活但独立。只有75行，包括MIT许可证信息、空白行和注释。接受标准数字格式，如#、##0.00或带否定的-000.####。接受任何国家/地区格式，如###0,00，#，###.##，#‘###.##或任何类型的非编号符号。接受任意数字分组。#、##、#0.000或#、####0.##均有效。接受任何冗余/防傻瓜格式。##、###、##。#或0#、#00####0#都正常。自动数字舍入。简单的界面，只需提供如下掩码和值：格式（“0.0000”，3.141592）

UPDATE这是我自己开发的应用程序，用于最常见的任务：

var NumUtil = {};

/**
  Petty print 'num' wth exactly 'signif' digits.
  pp(123.45, 2) == "120"
  pp(0.012343, 3) == "0.0123"
  pp(1.2, 3) == "1.20"
*/
NumUtil.pp = function(num, signif) {
    if (typeof(num) !== "number")
        throw 'NumUtil.pp: num is not a number!';
    if (isNaN(num))
        throw 'NumUtil.pp: num is NaN!';
    if (num < 1e-15 || num > 1e15)
        return num;
    var r = Math.log(num)/Math.LN10;
    var dot = Math.floor(r) - (signif-1);
    r = r - Math.floor(r) + (signif-1);
    r = Math.round(Math.exp(r * Math.LN10)).toString();
    if (dot >= 0) {
        for (; dot > 0; dot -= 1)
            r += "0";
        return r;
    } else if (-dot >= r.length) {
        var p = "0.";
        for (; -dot > r.length; dot += 1) {
            p += "0";
        }
        return p+r;
    } else {
        return r.substring(0, r.length + dot) + "." + r.substring(r.length + dot);
    }
}

/** Append leading zeros up to 2 digits. */
NumUtil.align2 = function(v) {
    if (v < 10)
        return "0"+v;
    return ""+v;
}
/** Append leading zeros up to 3 digits. */
NumUtil.align3 = function(v) {
    if (v < 10)
        return "00"+v;
    else if (v < 100)
        return "0"+v;
    return ""+v;
}

NumUtil.integer = {};

/** Round to integer and group by 3 digits. */
NumUtil.integer.pp = function(num) {
    if (typeof(num) !== "number") {
        console.log("%s", new Error().stack);
        throw 'NumUtil.integer.pp: num is not a number!';
    }
    if (isNaN(num))
        throw 'NumUtil.integer.pp: num is NaN!';
    if (num > 1e15)
        return num;
    if (num < 0)
        throw 'Negative num!';
    num = Math.round(num);
    var group = num % 1000;
    var integ = Math.floor(num / 1000);
    if (integ === 0) {
        return group;
    }
    num = NumUtil.align3(group);
    while (true) {
        group = integ % 1000;
        integ = Math.floor(integ / 1000);
        if (integ === 0)
            return group + " " + num;
        num = NumUtil.align3(group) + " " + num;
    }
    return num;
}

NumUtil.currency = {};

/** Round to coins and group by 3 digits. */
NumUtil.currency.pp = function(amount) {
    if (typeof(amount) !== "number")
        throw 'NumUtil.currency.pp: amount is not a number!';
    if (isNaN(amount))
        throw 'NumUtil.currency.pp: amount is NaN!';
    if (amount > 1e15)
        return amount;
    if (amount < 0)
        throw 'Negative amount!';
    if (amount < 1e-2)
        return 0;
    var v = Math.round(amount*100);
    var integ = Math.floor(v / 100);
    var frac = NumUtil.align2(v % 100);
    var group = integ % 1000;
    integ = Math.floor(integ / 1000);
    if (integ === 0) {
        return group + "." + frac;
    }
    amount = NumUtil.align3(group);
    while (true) {
        group = integ % 1000;
        integ = Math.floor(integ / 1000);
        if (integ === 0)
            return group + " " + amount + "." + frac;
        amount = NumUtil.align3(group) + " " + amount;
    }
    return amount;
}

PatrickDesjardins的回答看起来不错，但我更喜欢简单的JavaScript代码。下面是我刚刚编写的一个函数，用于输入一个数字并以货币格式返回（减去美元符号）：

// Format numbers to two decimals with commas
function formatDollar(num) {
    var p = num.toFixed(2).split(".");
    var chars = p[0].split("").reverse();
    var newstr = '';
    var count = 0;
    for (x in chars) {
        count++;
        if(count%3 == 1 && count != 1) {
            newstr = chars[x] + ',' + newstr;
        } else {
            newstr = chars[x] + newstr;
        }
    }
    return newstr + "." + p[1];
}