JavaScript 格式化数字、金额、千分位、保留几位小数、舍入舍去…

    <script type = "text/javascript">
		function number_format(number, decimals, dec_point, thousands_sep,roundtag) {
		    /*
		    * 参数说明：
		    * number：要格式化的数字
		    * decimals：保留几位小数
		    * dec_point：小数点符号
		    * thousands_sep：千分位符号
		    * roundtag:舍入参数，默认 "ceil" 向上取,"floor"向下取,"round" 四舍五入
		    * */
		    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);
		}
    </script>

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"