We can use the call() method to copy over properties from one constructor into another constructor. Let’s create a Warrior and a Healer constructor.

Even if it's const, an object can still have properties added later returning any arbitrary type. Indexing into the object would then have to return any - and that's an implicit any.

fresh (i.e. provably do not have properties we don't know about)

in languages (like JavaScript and Java) where external objects do have direct access to instance vars

In case you need to verify that object is instance of particular class you have to check constructor with your particular class

for (var member in myObject) delete myObject[member]; ...would seem to be pretty effective in cleaning the object in one line of code

for (var prop in obj) { if (obj.hasOwnProperty(prop)) { delete obj[prop]; } }

I forgot to mention in the original issue way back that I have a lot of data. Like 1 to 3 MB that is being passed around via export let foo.

Object.keys(obj).forEach could work, but it only includes own properties; for…in includes enumerable properties anywhere on the prototype chain.

Object.filter = (obj, predicate) => Object.fromEntries(Object.entries(obj).filter(predicate))

Using reduce and Object.keys As (1), in combination with Object.assign Using map and spread syntax instead of reduce Using Object.entries and Object.fromEntries