OpenCV
4.1.0
Open Source Computer Vision

Scalar is array type in Javascript. Point, Size, Circle, Rect and RotatedRect are object type in JavaScript.
There are 2 ways to construct a Point and they are the same:
x  x coordinate of the point.(the origin is the top left corner of the image) 
y  y coordinate of the point. 
There are 2 ways to construct a Scalar and they are the same:
R  pixel value of red channel. 
G  pixel value of green channel. 
B  pixel value of blue channel. 
Alpha  pixel value of alpha channel. 
There are 2 ways to construct a Size and they are the same:
width  the width of the size. 
height  the height of the size. 
There are 2 ways to construct a Circle and they are the same:
center  the center of the circle. 
radius  the radius of the circle. 
There are 2 ways to construct a Rect and they are the same:
x  x coordinate of the vertex which is the top left corner of the rectangle. 
y  y coordinate of the vertex which is the top left corner of the rectangle. 
width  the width of the rectangle. 
height  the height of the rectangle. 
There are 2 ways to construct a RotatedRect and they are the same:
center  the rectangle mass center. 
size  width and height of the rectangle. 
angle  the rotation angle in a clockwise direction. When the angle is 0, 90, 180, 270 etc., the rectangle becomes an upright rectangle. 
Learn how to get the vertices from rotatedRect:
We use the function: cv.RotatedRect.points(rotatedRect)
rotatedRect  rotated rectangle 
Learn how to get the bounding rectangle from rotatedRect:
We use the function: cv.RotatedRect.boundingRect(rotatedRect)
rotatedRect  rotated rectangle 