x

A number.

The inverse tangent (angle in radians between $-\frac{\pi}{2}$ and $\frac{\pi}{2}$, inclusive) of x. If x is Infinity, it returns $\frac{\pi}{2}$. If x is -Infinity, it returns $-\frac{\pi}{2}$.

Because atan() is a static method of Math, you always use it as Math.atan(), rather than as a method of a Math object you created (Math is not a constructor).

Math.atan(-Infinity); // -1.5707963267948966 (-π/2)
Math.atan(-0); // -0
Math.atan(0); // 0
Math.atan(1); // 0.7853981633974483  (π/4)
Math.atan(Infinity); // 1.5707963267948966  (π/2)

// The angle that the line (0,0) -- (x,y) forms with the x-axis in a Cartesian coordinate system
const theta = (x, y) => Math.atan(y / x);

Note that you may want to avoid the theta function and use Math.atan2() instead, which has a wider range (between -π and π) and avoids outputting NaN for cases such as when x is 0.

• Math.acos()
• Math.asin()
• Math.atan2()
• Math.cos()
• Math.sin()
• Math.tan()