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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; | |
}; |
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