这里有一个简单的函数，它为千个分隔符插入逗号。它使用数组函数而不是RegEx。

/**
 * Format a number as a string with commas separating the thousands.
 * @param num - The number to be formatted (e.g. 10000)
 * @return A string representing the formatted number (e.g. "10,000")
 */
var formatNumber = function(num) {
    var array = num.toString().split('');
    var index = -3;
    while (array.length + index > 0) {
        array.splice(index, 0, ',');
        // Decrement by 4 since we just added another unit to the array.
        index -= 4;
    }
    return array.join('');
};

CodeSandbox链接，示例如下：https://codesandbox.io/s/p38k63w0vq

在这里没有找到一个现代和全面的解决方案之后，我编写了一个箭头函数（没有正则表达式）来解决格式化问题，它允许调用者为欧洲和世界其他地区提供小数位数以及句点和千位分隔符。

示例：数字格式化程序（1234567890.123456）=>1234567890数字格式化程序（1234567890.123456，4）=>1234567890.1235numberFormatter（1234567890.123456，4，'.'，'，'）=>1.234.567.8901235欧洲

以下是用ES6（现代语法）编写的函数：

const numberFormatter = (number, fractionDigits = 0, thousandSeperator = ',', fractionSeperator = '.') => {
    if (number!==0 && !number || !Number.isFinite(number)) return number
    const frDigits = Number.isFinite(fractionDigits)? Math.min(Math.max(fractionDigits, 0), 7) : 0
    const num = number.toFixed(frDigits).toString()

    const parts = num.split('.')
    let digits = parts[0].split('').reverse()
    let sign = ''
    if (num < 0) {sign = digits.pop()}
    let final = []
    let pos = 0

    while (digits.length > 1) {
        final.push(digits.shift())
        pos++
        if (pos % 3 === 0) {final.push(thousandSeperator)}
    }
    final.push(digits.shift())
    return `${sign}${final.reverse().join('')}${frDigits > 0 ? fractionSeperator : ''}${frDigits > 0 && parts[1] ? parts[1] : ''}`
}

它已被测试为阴性、不良输入和NaN病例。如果输入是NaN，则只需返回它。

这里有一个简单的可重用函数，它返回具有指定小数位数的字符串，并允许您切换逗号的包含。

function format_number(number, num_decimals, include_comma)
{
    return number.toLocaleString('en-US', {useGrouping: include_comma, minimumFractionDigits: num_decimals, maximumFractionDigits: num_decimals});
}

用法示例：

format_number(1234.56789, 2, true); // Returns '1,234.57'
format_number(9001.42, 0, false); // Returns '9001'

如果需要进一步自定义字符串，可以在此处找到格式选项列表。

以下代码使用字符扫描，因此没有正则表达式。

function commafy( num){
  var parts = (''+(num<0?-num:num)).split("."), s=parts[0], L, i=L= s.length, o='';
  while(i--){ o = (i===0?'':((L-i)%3?'':',')) 
                  +s.charAt(i) +o }
  return (num<0?'-':'') + o + (parts[1] ? '.' + parts[1] : ''); 
}

它显示出令人期待的性能：http://jsperf.com/number-formatting-with-commas/5

2015.4.26:在num<0时解决问题的小修复。看见https://jsfiddle.net/runsun/p5tqqvs3/

我已经调整了您的代码以在TextBox（输入类型=“text”）中工作，这样我们就可以在不丢失光标的情况下实时输入和删除数字。如果您在删除时选择范围，它也会起作用。您可以自由使用箭头和起始/结束按钮。谢谢你节省了我的时间！

//function controls number format as "1,532,162.3264321"
function numberWithCommas(x) {
    var e = e || window.event;
    if (e.keyCode >= '35' && e.keyCode <= '40') return; //skip arrow-keys
    var selStart = x.selectionStart, selEnd = x.selectionEnd; //save cursor positions
    var parts = x.value.toString().split(".");
    var part0len = parts[0].length; //old length to check if new ',' would be added. Need for correcting new cursor position (+1 to right).

    //if user deleted ',' - remove previous number instead (without selection)
    if (x.selectionLength == 0 && (e.keyCode == 8 || e.keyCode == 46)) {//if pressed 8-backspace or 46-delete button
        var delPos = parts[0].search(/\d{4}/);
        if (delPos != -1) {//if found 4 digits in a row (',' is deleted)
            if (e.keyCode == 8) {//if backspace flag
                parts[0] = parts[0].slice(0, selStart - 1) + parts[0].slice(selEnd, parts[0].length);
                selEnd--;
                if (selStart > selEnd) selStart = selEnd;
            } else {
                parts[0] = parts[0].slice(0, selStart) + parts[0].slice(selEnd + 1, parts[0].length);
                selStart++;
                if (selEnd < selStart) selEnd = selStart;
            }
        }
    }

   var hasMinus = parts[0][0] == '-';
   parts[0] = (hasMinus ? '-' : '') + parts[0].replace(/[^\d]*/g, ""); //I'd like to clear old ',' to avoid things like 1,2,3,5,634.443216
   parts[0] = parts[0].replace(/\B(?=(\d{3})+(?!\d))/g, ","); //sets ',' between each 3 digits
   if (part0len < parts[0].length) { //move cursor to right if added new ','
       selStart++;
       selEnd++;
   } else if (part0len > parts[0].length) { //..or if removed last one ','
       selStart--;
       selEnd--;
   }
   x.value = parts.join(".");
   x.setSelectionRange(selStart, selEnd); //restoring cursor position
}
function saveSelectionLength(x) {
    x.selectionLength = x.selectionEnd - x.selectionStart;
}

要使用它，只需添加两个事件-onKeyUp和onKeyDown

<asp:TextBox runat="server" ID="val" Width="180px" onKeyUp="numberWithCommas(this);" onKeyDown="saveSelectionLength(this);"/>

我想我应该分享一个小技巧，我正在使用它来格式化大数字。我没有插入逗号或空格，而是在“千”之间插入一个空的但可见的跨度。这使得数千个输入很容易看到，但它允许以原始格式复制/粘贴输入，不使用逗号/空格。

// This function accepts an integer, and produces a piece of HTML that shows it nicely with 
// some empty space at "thousand" markers. 
// Note, these space are not spaces, if you copy paste, they will not be visible.
function valPrettyPrint(orgVal) {
  // Save after-comma text, if present
  var period = orgVal.indexOf(".");
  var frac = period >= 0 ? orgVal.substr(period) : "";
  // Work on input as an integer
  var val = "" + Math.trunc(orgVal);
  var res = "";
  while (val.length > 0) {
    res = val.substr(Math.max(0, val.length - 3), 3) + res;
    val = val.substr(0, val.length - 3);
    if (val.length > 0) {
        res = "<span class='thousandsSeparator'></span>" + res;
    }
  }
  // Add the saved after-period information
  res += frac;
  return res;
}

使用此CSS：

.thousandsSeparator {
  display : inline;
  padding-left : 4px;
}

请参见示例JSFiddle。