hashmap VS immutable-js

Glad to see this make it into the core.

I've been using this library for ages now...

https://github.com/cornelk/hashmap

Always entertains me to see developers write all the lock/unlock code when they could just use that.

Assuming it is issue 54 and its age, I am now unsure about the usability.

Pre-allocating would not fix https://github.com/cornelk/hashmap/issues/47 as the bug is in the linked list. This is not grow related but an issue with concurrent Add/Delete on the list.

Would be interesting to compare with https://github.com/cornelk/hashmap

immutable for JavaScript.

Check out Object.freeze. There's also Immutable.js for working with immutable data.

Use immutability to manage state updates When updating state in your React application, it's important to ensure that you are not mutating the original state object. Instead, you should create a new copy of the state object with the updated values. Immutability makes it easier to manage state updates and ensures that the updates are performed in a predictable and safe manner. Libraries like Immutable.js provide a set of functions that simplify working with immutable data in React applications.

Enter Immutable.js, a library for creating and updating immutable state in JavaScript. With usual mutable JavaScript objects you might write something like:

The Immutable.js README has a much more complete description of immutability and why you might want to use the library. Also worth mentioning that Immer is an alternative which is a bit easier to get started with.

Examples: immutable-js Immer

I can't speak to C# and Java, but the suggestion in this post: ImmutableJS already uses Persistent data structures. (It's the second sentence of their introduction)

feed.feedManager.state.activities is an immutable Map (created with Immutabe.js), so you get the activity object using getIn and toJS methods.

You could create explicitly immutable references and state by using a tool like Immer.js or Immutable.js and do something like your example using their API.