Math.acos()

Baseline Widely available

This feature is well established and works across many devices and browser versions. It’s been available across browsers since July 2015.

Math.acos() 靜態方法會回傳一個數值的反餘弦值(以弧度表示)。也就是說,

x[1,1],𝙼𝚊𝚝𝚑.𝚊𝚌𝚘𝚜(𝚡)=arccos(x)=the unique y[0,π] such that cos(y)=x\forall x \in [{-1}, 1],\;\mathtt{\operatorname{Math.acos}(x)} = \arccos(x) = \text{the unique } y \in [0, \pi] \text{ such that } \cos(y) = x

嘗試一下

// Calculates angle of a right-angle triangle in radians
function calcAngle(adjacent, hypotenuse) {
  return Math.acos(adjacent / hypotenuse);
}

console.log(calcAngle(8, 10));
// Expected output: 0.6435011087932843

console.log(calcAngle(5, 3));
// Expected output: NaN

語法

js
Math.acos(x)

參數

x

一個介於 -1 和 1(包含邊界)的數字,代表角度的餘弦值。

回傳值

x 的反餘弦值(0 到 π 之間的角度,以弧度表示,包含邊界)。如果 x 小於 -1 或大於 1,則回傳 NaN

描述

由於 acos()Math 的靜態方法,你必須使用 Math.acos() 來呼叫它,而非呼叫你建立的 Math 物件的方法(Math 並非建構子)。

範例

使用 Math.acos()

js
Math.acos(-2); // NaN
Math.acos(-1); // 3.141592653589793 (π)
Math.acos(0); // 1.5707963267948966 (π/2)
Math.acos(0.5); // 1.0471975511965979 (π/3)
Math.acos(1); // 0
Math.acos(2); // NaN

規範

Specification
ECMAScript® 2025 Language Specification
# sec-math.acos

瀏覽器相容性

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Chrome
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Firefox for Android
Opera Android
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Samsung Internet
WebView Android
WebView on iOS
Deno
Node.js
acos

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Full support
Full support

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