How to easily insert new property in a Map object at specific position(index).

For example I have Map object with more than 1000 key-value pairs and I want to one more at position 235.

object type Map

{
 1a001: {...},
 1a002: {...},
 1a003: {...},
 <--- insert item at position n
 ... 1000 of items
 1a1001: {...},
 1a1002: {...},
}

Something like

mapObject.insert({ ...someobject}, property, index)