JS实现数字千位符格式化方法

/**
 * [number_format 参数说明：]
 * @param  {[type]} number        [number：要格式化的数字]
 * @param  {[type]} decimals      [decimals：保留几位小数]
 * @param  {[type]} dec_point     [dec_point：小数点符号]
 * @param  {[type]} thousands_sep [thousands_sep：千分位符号]
 * @param  {[type]} roundtag      [roundtag:舍入参数，默认 "ceil" 向上取,"floor"向下取,"round" 四舍五入]
 * @return {[type]}               [description]
 *    
 */
function number_format(number, decimals, dec_point, thousands_sep, roundtag) {

    number = (number + '').replace(/[^0-9+-Ee.]/g, '');
    roundtag = roundtag || "ceil"; //"ceil","floor","round"
    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);
            console.log();

            return '' + parseFloat(Math[roundtag](parseFloat((n * k).toFixed(prec * 2))).toFixed(prec * 2)) / k;
        };
    s = (prec ? toFixedFix(n, prec) : '' + Math.round(n)).split('.');
    var re = /(-?\d+)(\d{3})/;
    while (re.test(s[0])) {
        s[0] = s[0].replace(re, "$1" + sep + "$2");
    }

    if ((s[1] || '').length < prec) {
        s[1] = s[1] || '';
        s[1] += new Array(prec - s[1].length + 1).join('0');
    }
    return s.join(dec);
}
console.log(number_format(2, 2, ".", ",")) //"2.00"
console.log(number_format(3.7, 2, ".", ",")) //"3.70"
console.log(number_format(3, 0, ".", ",")) //"3"
console.log(number_format(9.0312, 2, ".", ",")) //"9.03"
console.log(number_format(9.00, 2, ".", ",")) //"9.00"
console.log(number_format(39.715001, 2, ".", ",", "floor")) //"39.71"
console.log(number_format(9.7, 2, ".", ",")) //"9.70"
console.log(number_format(39.7, 2, ".", ",")) //"39.70"
console.log(number_format(9.70001, 2, ".", ",")) //"9.71"
console.log(number_format(39.70001, 2, ".", ",")) //"39.71"
console.log(number_format(9996.03, 2, ".", ",")) //"9996.03"
console.log(number_format(1.797, 3, ".", ",", "floor")) //"1.797"