js中toFixed精度问题的解决办法

Number.prototype.toFixed = function (n) {

if (n > 20 || n < 0) {

throw new RangeError('toFixed() digits argument must be between 0 and 20');

}

const number = this;

if (isNaN(number) || number >= Math.pow(10, 21)) {

return number.toString();

}

if (typeof (n) == 'undefined' || n == 0) {

return (Math.round(number)).toString();

}

let result = number.toString();

const arr = result.split('.');

// 整数的情况

if (arr.length < 2) {

result += '.';

for (let i = 0; i < n; i += 1) {

result += '0';

}

return result;

}

const integer = arr[0];

const decimal = arr[1];

if (decimal.length == n) {

return result;

}

if (decimal.length < n) {

for (let i = 0; i < n - decimal.length; i += 1) {

result += '0';

}

return result;

}

result = integer + '.' + decimal.substr(0, n);

const last = decimal.substr(n, 1);

// 四舍五入，转换为整数再处理，避免浮点数精度的损失

if (parseInt(last, 10) >= 5) {

const x = Math.pow(10, n);

result = (Math.round((parseFloat(result) * x)) + 1) / x;

result = result.toFixed(n);

}

return result;

};

引自 : http://www.jianshu.com/p/849b0ae36b36