double atan(
num x
)

Converts x to a dobule and returns the arc tangent of the vlaue. Returns a value in the range -PI/2..PI/2, or NaN if x is NaN.

Source

/**
 * Converts [x] to a dobule and returns the arc tangent of the vlaue.
 * Returns a value in the range -PI/2..PI/2, or NaN if [x] is NaN.
 */
external double atan(num x);