Math.asin()

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.asin() 靜態方法回傳數字的反正弦值(單位為弧度)。也就是說,

x[1,1],𝙼𝚊𝚝𝚑.𝚊𝚜𝚒𝚗(𝚡)=arcsin(x)=the unique y[π2,π2] such that sin(y)=x\forall x \in [{-1}, 1],\;\mathtt{\operatorname{Math.asin}(x)} = \arcsin(x) = \text{the unique } y \in \left[-\frac{\pi}{2}, \frac{\pi}{2}\right] \text{ such that } \sin(y) = x

嘗試一下

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

console.log(calcAngle(6, 10));
// Expected output: 0.6435011087932844

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

語法

js
Math.asin(x)

參數

x

一個介於 -1 到 1 之間(包含邊界)的數字,表示角度的正弦值。

回傳值

x 的反正弦值(單位為弧度,範圍介於 -π2-\frac{\pi}{2}π2\frac{\pi}{2} 之間,包含邊界)。如果 x 小於 -1 或大於 1,則回傳 NaN

描述

由於 asin()Math 的靜態方法,你必須使用 Math.asin() 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.asin()

js
Math.asin(-2); // NaN
Math.asin(-1); // -1.5707963267948966 (-π/2)
Math.asin(-0); // -0
Math.asin(0); // 0
Math.asin(0.5); // 0.5235987755982989 (π/6)
Math.asin(1); // 1.5707963267948966 (π/2)
Math.asin(2); // NaN

規範

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

瀏覽器相容性

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asin

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Full support
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