toExponential()
method 用來將數字轉成「科學記數法」格式。
語法
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 |
|
小數點後的位數。需為 0 至 20 之間。 |
回傳直
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
- 若參數
fractionDigits
不是Number
,則觸發TypeError
。
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
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
Specifications
Specification | Status | Comment |
---|---|---|
ECMAScript 3rd Edition (ECMA-262) | Standard | Initial definition. Implemented in JavaScript 1.5. |
ECMAScript 5.1 (ECMA-262) The definition of 'Number.prototype.toExponential' in that specification. |
Standard | |
ECMAScript 2015 (6th Edition, ECMA-262) The definition of 'Number.prototype.toExponential' in that specification. |
Standard | |
ECMAScript Latest Draft (ECMA-262) The definition of 'Number.prototype.toExponential' in that specification. |
Draft |
瀏覽器支援度
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This compatibility table still uses the old format,
because we haven't yet converted the data it contains.
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Feature | Chrome | Firefox (Gecko) | Internet Explorer | Opera | Safari |
---|---|---|---|---|---|
Basic support | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) |
Feature | Android | Chrome for Android | Firefox Mobile (Gecko) | IE Mobile | Opera Mobile | Safari Mobile |
---|---|---|---|---|---|---|
Basic support | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) |