How To Reference Positions Of Other Entities In Polygon Hierarchy Of Cesium Using Javascript?

I am using Cesium to visualize my scenario and I want to create a polygon in JavaScript using position of other moving entities as references for its endpoints. As suggested in the

Solution 1:

Entity properties have a function getValue that takes a JulianDate time as a parameter and returns the value at that time. To get a position, you should be able to do something like

var position = entity.position.getValue(viewer.clock.currentTime);

Solution 2:

What worked for me in JavaScript was to define the positions property with new Cesium.PositionPropertyArray([]).

This post on Cesium's Community Forum by Scott_Hunter helped me, specifically the second link to Sandcastle.