js中toFixed的精度问题

// 解决不同浏览器对toFixed进行四舍五入會造成精度問題
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();
	}
	
	var 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;
}