Slingshot example with Keys and Constraint, instead of MouseConstraint and Mouse

[hacktronics]

I want to adapt the slingshot example with keys instead of mouse, while using the constraint. I don't have a canvas, I use Matter JS to get the position and update the body position is my application (which is not matterJS canvas). So matterJS is just used for physics calculation and there is no mouse drag and drop support in my application.

When I add a new BodyB to the elastic constraint, the position of the ball does not changes? I want to adopt the slingshot example for education purpose. I can see another question, but I don't want to manually apply force, the goal is to adapt the constraint without using mouse.