JavaScript Math.sin()

Math.sin(x) returns the sine of an angle measured in radians. If your input is in degrees, convert it to radians before calling Math.sin().

console.log(Math.sin(Math.PI / 2)); // 1
console.log(Math.sin(90 * Math.PI / 180)); // 1

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Math.sin() syntax Top ↑

Math.sin(angleInRadians)

Math.sin() expects radians, not degrees Top ↑

Passing 90 directly means 90 radians, not 90 degrees. That is why Math.sin(90) is not 1.

console.log(Math.sin(90)); // about 0.8939966636

Common angles in radians Top ↑

console.log(Math.sin(0));                 // 0
console.log(Math.sin(Math.PI / 2));       // 1
console.log(Math.sin(Math.PI));           // approximately 0
console.log(Math.sin(3 * Math.PI / 2));   // -1
console.log(Math.sin(2 * Math.PI));       // approximately 0

Convert degrees to radians Top ↑

function degreesToRadians(degrees) {
  return degrees * (Math.PI / 180);
}
console.log(Math.sin(degreesToRadians(90)));  // 1
console.log(Math.sin(degreesToRadians(270))); // -1

Why sin(π) may not display exactly 0 Top ↑

Math.PI and the result are floating-point approximations. A tiny value such as 1.2246467991473532e-16 is effectively very close to zero but not represented as exact zero.

Return range and invalid inputs Top ↑

console.log(Math.sin(Infinity)); // NaN
console.log(Math.sin(NaN));      // NaN

For finite numeric inputs, the return value is between -1 and 1.

Using sine for circular movement Top ↑

const angle = Math.PI / 6;
const radius = 10;
const y = Math.sin(angle) * radius;
console.log(y); // about 5

Math.abs() →

Subhendu Mohapatra

Author & Instructor at plus2net

I write and maintain practical tutorials on Python, PHP, SQL, JavaScript, HTML, jQuery, and web development at plus2net. The tutorials focus on clear explanations, working examples, and code that readers can test and adapt while learning.

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