1 四舍五入
eg: (1.23).round() = 1.2
(1.2456).round(3) = 1.246
if (!Number.prototype.round) { ???Number.prototype.round = function (count) { ???????var res = 0; ???????var val = this.toString(); ???????var num = parseInt(count || 2); ???????var dataArr = val.split(‘.‘); ???????var arr1 = dataArr[0] || ""; ???????var arr2 = dataArr[1] || ""; ???????var newArr2 = arr2; ???????if (arr2.length > num) { ???????????var lastNum = arr2.substring(num, num + 1); ???????????if (parseInt(lastNum) >= 5) { ???????????????newArr2 = parseInt(newArr2.substring(0, num)) + 1; ???????????????newArr2 = newArr2.toString(); ???????????????if (newArr2.length < num) { ???????????????????for (var i = 0; i < (num - newArr2.length); i++) { ???????????????????????newArr2 = "0" + newArr2; ???????????????????} ???????????????} ???????????} ???????} ???????val = parseFloat(arr1 + ‘.‘ + newArr2); ???????res = parseFloat(val.toFixed(num)); ???????return res; ???}}2 加减乘除
eg: (1).plus(2) = 3
if (!Number.prototype.plus) { //‘+‘ ???Number.prototype.plus = function (addend) { ???????var arg1 = this, ???????????arg2 = addend; ???????var r1, ???????????r2, ???????????m, ???????????num1, ???????????num2; ???????try { ???????????r1 = arg1.toString().split(".")[1].length; ???????} catch (e) { ???????????r1 = 0 ???????} ???????try { ???????????r2 = arg2.toString().split(".")[1].length; ???????} catch (e) { ???????????r2 = 0 ???????} ???????m = Math.pow(10, Math.max(r1, r2)); ???????num1 = r1 == 0 ? parseInt(arg1 * m) : (parseInt(`${arg1.toString().replace(‘.‘, ‘‘)}`) * m / (Math.pow(10, r1))); ???????num2 = r2 == 0 ? parseInt(arg2 * m) : (parseInt(`${arg2.toString().replace(‘.‘, ‘‘)}`) * m / (Math.pow(10, r2))); ???????return (num1 + num2) / m; ???}}if (!Number.prototype.minus) { //‘-‘ ???Number.prototype.minus = function (Subtraction) { ???????var arg1 = this, ???????????arg2 = Subtraction; ???????var r1, ???????????r2, ???????????m, ???????????n, ???????????num1, ???????????num2; ???????try { ???????????r1 = arg1.toString().split(".")[1].length ???????} catch (e) { ???????????r1 = 0 ???????} ???????try { ???????????r2 = arg2.toString().split(".")[1].length ???????} catch (e) { ???????????r2 = 0 ???????} ???????m = Math.pow(10, Math.max(r1, r2)); ???????n = (r1 >= r2) ? r1 : r2; ???????num1 = r1 == 0 ? parseInt(arg1 * m) : (parseInt(`${arg1.toString().replace(‘.‘, ‘‘)}`) * m / (Math.pow(10, r1))); ???????num2 = r2 == 0 ? parseInt(arg2 * m) : (parseInt(`${arg2.toString().replace(‘.‘, ‘‘)}`) * m / (Math.pow(10, r2))); ???????return parseFloat(((num1 - num2) / m).toFixed(n)); ???}}if (!Number.prototype.multiply) { //‘*‘ ???Number.prototype.multiply = function (multiple) { ???????var arg1 = this, ???????????arg2 = multiple; ???????var m = 0, ???????????s1 = arg1.toString(), ???????????s2 = arg2.toString(); ???????try { ???????????m += s1.split(".")[1].length ???????} catch (e) { } ???????try { ???????????m += s2.split(".")[1].length ???????} catch (e) { } ???????return Number(s1.replace(".", "")) * Number(s2.replace(".", "")) / Math.pow(10, m) ???} ???if (!Number.prototype.devide) { //‘/‘ ???????Number.prototype.devide = function (divisor) { ???????????var arg1 = this, ???????????????arg2 = divisor; ???????????var t1 = 0, ???????????????t2 = 0, ???????????????r1, ???????????????r2; ???????????try { ???????????????t1 = arg1.toString().split(".")[1].length ???????????} catch (e) { } ???????????try { ???????????????t2 = arg2.toString().split(".")[1].length ???????????} catch (e) { } ???????????r1 = Number(arg1.toString().replace(".", "")) ???????????r2 = Number(arg2.toString().replace(".", "")) ???????????return (r1 / r2).multiply(Math.pow(10, t2 - t1)); ???????} ???}}if (!Number.prototype.round) { Number.prototype.round = function (count) { var res = 0; var val = this.toString(); var num = parseInt(count || 2); var dataArr = val.split(‘.‘); var arr1 = dataArr[0] || ""; var arr2 = dataArr[1] || ""; var newArr2 = arr2; if (arr2.length > num) { var lastNum = arr2.substring(num, num + 1); if (parseInt(lastNum) >= 5) { newArr2 = parseInt(newArr2.substring(0, num)) + 1; newArr2 = newArr2.toString(); if (newArr2.length < num) { for (var i = 0; i < (num - newArr2.length); i++) { newArr2 = "0" + newArr2; } } } }
val = parseFloat(arr1 + ‘.‘ + newArr2); res = parseFloat(val.toFixed(num)); return res; }}
js 加减乘除以及四舍五入 新写法
原文地址：https://www.cnblogs.com/zxhome/p/10342313.html