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 = 0i <ni += 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 = 0i <n - decimal.lengthi += 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 正数+1 负数-1
if (parseInt(last, 10) >= 5) {
const x = Math.pow(10, n)
result = (Math.round((parseFloat(result) * x)) + (parseFloat(result) >0 ? 1 : -1)) / x
result = result.toFixed(n)
}
return result
}
toFixed()方法可把
Number
四舍五入为指定小数位数的数字。在JS中函数
toFixed(n)的参数n为要保留的小数位数，且n为0~20，当n超过20的时候，JS会出错。
