toFixed()四舍五入的不准确性

chrome下的测试结果：

修正方案：

    <script>
        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);
                console.log(x, parseFloat(result))
                result = (Math.round((parseFloat(result) * x)) + 1) / x;
                result = result.toFixed(n);
            }
            return result;
        }
    </script>