jsPlumb anchor array quick reference - https://jsplumbtoolkit.com/community/doc/anchors.html

anchor.js

/* Anchor array: [ x, y, dx, dy ]
x, y (close of square): position on node, 0.0 to 1.0
dx, dy (end of arrows): direction, -1, 0 or 1

                  0,-1
                   ^
                   |
                   +
           0,0   0.5,0    1,0
              +----------+
              |          |
              |          |
-1,0 <-+ 0,0.5|          |1,0.5 +-> 1,0
              |          |
              |          |
              +----------+
           0,1   0.5,1    1,1
                   +
                   |
                   v
                  0,1
*/