Number.prototype.toExponential()

toExponential() method 用來將數字轉成「科學記數法」格式。

語法

js
numObj.toExponential([fractionDigits])

參數

參數 可選 默認值 類型 說明
fractionDigits ● 默認盡可能將數字完整顯示 Number（正整數） 小數點後的位數。需為 0 至 20 之間。

回傳值

一 string，將數字以「科學計數法」格式表示出來

Exceptions

RangeError

若 fractionDigits 超出範圍（可接受的範圍是 0 ～ 20 之間的正整數）觸發 RangeError。

TypeError (en-US)

若參數 fractionDigits 不是 Number，則觸發TypeError (en-US)。

Description

If the fractionDigits argument is omitted, the number of digits after the decimal point defaults to the number of digits necessary to represent the value uniquely.

If you use the toExponential() method for a numeric literal and the numeric literal has no exponent and no decimal point, leave whitespace(s) before the dot that precedes the method call to prevent the dot from being interpreted as a decimal point.

If a number has more digits than requested by the fractionDigits parameter, the number is rounded to the nearest number represented by fractionDigits digits. See the discussion of rounding in the description of the toFixed() method, which also applies to toExponential().

範例

Using toExponential

js
var numObj = 77.1234;

console.log(numObj.toExponential()); // logs 7.71234e+1
console.log(numObj.toExponential(4)); // logs 7.7123e+1
console.log(numObj.toExponential(2)); // logs 7.71e+1
console.log((77.1234).toExponential()); // logs 7.71234e+1
console.log((77).toExponential()); // logs 7.7e+1

規範

Specification
ECMAScript Language Specification
# sec-number.prototype.toexponential

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