JavaScript 数字格式化函数

以下是4个有用的JS数字格式化函数   
1. 四舍五入  
下面两个函数都能对浮点数进行四舍五入，保留小数点后两位。 

2. 给数字添加逗号  
每三位数字添加一个逗号，方便阅读 

3. 类似PHP的 number_format 功能  
这个函数可以添加分隔逗号或者进行四舍五入。 

4. 添加序数词  
给数字添加"st, nd, rd, th"等序数词。 

1.四舍五入 

/** 下面两个函数都能对浮点数进行四舍五入，保留小数点后两位 **/
 
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;
}
  
/**
*   Usage:  CurrencyFormatted(12345.678);
*   result: 12345.68
**/
 
function format_number(pnumber,decimals){
    if (isNaN(pnumber)) { return 0};
    if (pnumber=='') { return 0};
      
    var snum = new String(pnumber);
    var sec = snum.split('.');
    var whole = parseFloat(sec[0]);
    var result = '';
      
    if(sec.length > 1){
        var dec = new String(sec[1]);
        dec = String(parseFloat(sec[1])/Math.pow(10,(dec.length - decimals)));
        dec = String(whole + Math.round(parseFloat(dec))/Math.pow(10,decimals));
        var dot = dec.indexOf('.');
        if(dot == -1){
            dec += '.';
            dot = dec.indexOf('.');
        }
        while(dec.length <= dot + decimals) { dec += '0'; }
        result = dec;
    } else{
        var dot;
        var dec = new String(whole);
        dec += '.';
        dot = dec.indexOf('.');    
        while(dec.length <= dot + decimals) { dec += '0'; }
        result = dec;
    }  
    return result;
}
  
/**
*   Usage:  format_number(12345.678, 2);
*   result: 12345.68
**/

2.给数字添加逗号 

/** 每三位数字添加一个逗号，方便阅读 **/
 
function CommaFormatted(amount) {
    var delimiter = ","; // replace comma if desired
    amount = new String(amount);
    var a = amount.split('.',2)
    var d = a[1];
    var i = parseInt(a[0]);
    if(isNaN(i)) { return ''; }
    var minus = '';
    if(i < 0) { minus = '-'; }
    i = Math.abs(i);
    var n = new String(i);
    var a = [];
    while(n.length > 3)
    {
        var nn = n.substr(n.length-3);
        a.unshift(nn);
        n = n.substr(0,n.length-3);
    }
    if(n.length > 0) { a.unshift(n); }
    n = a.join(delimiter);
    if(d.length < 1) { amount = n; }
    else { amount = n + '.' + d; }
    amount = minus + amount;
    return amount;
}
  
/**
*   Usage:  CommaFormatted(12345678);
*   result: 12,345,678
**/
 
function addCommas(nStr) {
    nStr += '';
    var x = nStr.split('.');
    var x1 = x[0];
    var x2 = x.length >; 1 ? '.' + x[1] : '';
    var rgx = /(d+)(d{3})/;
      
    while (rgx.test(x1)) {
        x1 = x1.replace(rgx, '$1' + ',' + '$2');
    }
      
    return x1 + x2;
}
  
/**
*   Usage:  addCommas(12345678);
*   result: 12,345,678
**/

3.类似PHP的 number_format 功能

/** 这个函数可以添加分隔逗号或者进行四舍五入。 **/
 
function number_format (number, decimals, dec_point, thousands_sep) {
  
    number = (number + '').replace(/[^0-9+-Ee.]/g, '');
    var n = !isFinite(+number) ? 0 : +number,
        prec = !isFinite(+decimals) ? 0 : Math.abs(decimals),
        sep = (typeof thousands_sep === 'undefined') ? ',' : thousands_sep,
        dec = (typeof dec_point === 'undefined') ? '.' : dec_point,
        s = '',
        toFixedFix = function (n, prec) {
            var k = Math.pow(10, prec);
            return '' + Math.round(n * k) / k;
        };
    // Fix for IE parseFloat(0.55).toFixed(0) = 0;
    s = (prec ? toFixedFix(n, prec) : '' + Math.round(n)).split('.');
    if (s[0].length > 3) {
        s[0] = s[0].replace(/B(?=(?:d{3})+(?!d))/g, sep);
    }
    if ((s[1] || '').length < prec) {
        s[1] = s[1] || '';
        s[1] += new Array(prec - s[1].length + 1).join('0');
    }
    return s.join(dec);
}
  
/**
*   Usage:  number_format(123456.789, 2, '.', ',');
*   result: 123,456.79
**/

4.添加序数词 

/** 给数字添加"st, nd, rd, th"等序数词。 **/
 
Number.prototype.toOrdinal = function() {
    var n = this % 100;
    var suffix = ['th', 'st', 'nd', 'rd', 'th'];
    var ord = n < 21 ? (n < 4 ? suffix[n] : suffix[0]) : (n % 10 > 4 ? suffix[0] : suffix[n % 10]);
    return this + ord;
}
  
/*
*   Usage:
*   var myNumOld = 23
*   var myNumNew = myNumOld.toOrdinal()
*   Result: 23rd
*/

转自：http://www.oschina.net/code/snippet_28_7073