JavaScript Math atan2()

let num = Math.atan2(4, 3);
console.log(num); 

// Output: 0.9272952180016122

atan2() Syntax

The syntax of the atan2() method is:

Math.atan2(x, y)

Here, tan() is a static method. Hence, we are accessing the method using the class name, Math.

atan2() Parameters

The atan2() method takes two parameters:

• x - number, which is divided by the parameter y
• y - number that divides the parameter x

Here, the method computes the arctangent of x / y.

atan2() Return Value

The method returns:

• angle (in radians) after computing the arctan of x / y
• NaN (Not a Number) for non-numeric arguments x and y

Note: The returned angle will always be in the range -π to π for numeric arguments.

Example 1: JavaScript Math.atan2()

// compute the arctangent of 5 / 2
let result1 = Math.atan2(5, 2);
console.log(result1);    

// compute the arctangent of 0 / 5
let result2 = Math.atan(0, 5);
console.log(result2); 

// Output:
// 1.1902899496825317
 // 0

In the above example,

• Math.atan2(5, 2) - computes the arctan of 2.5 ( 5 / 2 )
• Math.atan2(0, 5) - computes the arctan of 0 ( 0 / 5 )

Example 2: Math.atan2() with Infinity

// atan2() with positive infinity
let num = Math.atan2(Infinity, 0);
console.log(num);   

// atan2() with negative infinity 
let num = Math.atan2(-Infinity, 0);
console.log(num);    

// atan2() with both infinities
let num = Math.atan2(Infinity, -Infinity);
console.log(num); 

// Output:
// 1.5707963267948966 (π/2)
// -1.5707963267948966 (-π/2)
// 2.356194490192345 (3*π/4)

Here, you can see we have successfully used the atan2() method with infinity. And the result is still between -π and π even though we have used it with infinity.

Example 3: Math.atan2() with Non-Numeric Arguments

// string variables
let str1 = "John";
let str2 = "Wick";

// atan2() with string arguments
let result = Math.atan2(str1, str2);
console.log(result);

// Output: NaN

The code above shows the use of the atan2() method with string arguments. That's why we get NaN as output.

Recommended readings:

• JavaScript Math tan()
• JavaScript Math atan()