Number.prototype.toFixed = function (n) { if (n > 20 || n < 0) { thrownewRangeError('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); }