Converting Object to Map using Generics
A few points first.


Avoid any like the plague. You can nearly always figure out a better type. When dealing with a JSON serialized data, I like to have a function similar to this to get rid of any as soon as possible:

function verify&lt;T&gt;(obj: any, fallback: T, isT: (obj: any) =&gt; obj is T): T {
  return isT(obj) ? obj : fallback;
}

Object.keys and Object.entries are a better fit for looping through an object if you are going to check hasOwnProperty. I prefer Object.entries when possible, if you have the browser support.
Choose const or let, don't mix them without good reason. const can result in better type inference so I prefer to use it when possible.


Here is how I would implement this function.

function convertObjectToMap&lt;In, Out&gt;(
  obj: { [K: string]: In } | undefined | null,
  classOfIn: new (v: In) =&gt; Out
): Map&lt;string, Out&gt; {
  const result = new Map&lt;string, Out&gt;();

  for (const [key, val] of Object.entries(obj || {})) {
    result.set(key, new classOfIn(val));
  }

  return result;
}