@jaenster/weakrefmap

WeakMap but completed

Weak references are great, but nearly nothing truly uses it in javascript.

WeakRefMap.

Why not just use WeakMap? A native WeakMap is write only, you cant do things like .forEach or for (const value of map). The only thing it can be used for is seeing if it contains it.

Example

import {WeakRefMap} from "weakrefmap";


class Clients {
    constructor(private readonly server: Server) {
    }

    doSomething() {

    }
}

class Server {
    clients = new WeakRefMap<string, Client>();
}

function test() {
    const server = new Server();
    let alice = new Client(server);
    const bob = new Client(server);
    server.clients.set('alice', alice).add('bob', bob);

    server.clients.forEach(client => client.doSomething());
    
    alice = null;
    // Alice is still floating in memory
    if (server.clients.has('alice')) {
      const lostAlice = server.clients.get('alice')
    }
}

test();

If this code was written with a normal new Map<string, Client>, everything would float forever in memory and never be cleaned. As both Client as Server have recursive references to each other. The magic of a weak reference will overcome this issue.

In the past, we would have demanded the user to call some server.close() function, but as we (java|type)script developers are lazy and not used with dealing with the garbage collector, we often forget.

With WeakRefMap the following happen

1. End of test(), reference all references to the client (clientA, clientB) get marked as deletable. As the variables are the only ones that count. The weak ref map is not counted as a reference
2. All Client instances get deleted
3. All server references are gone now, as test()'s server variable is gone, and so are all Client objects are gone
4. All memory usage of test() is fully and automatically cleaned up

What happens with a typical Map?

1. End of test(), references to the clientA and clientB are still holden in the Server instance.
2. clients instances still exists
3. server reference still exists in clients
4. all memory of test() is still in memory
5. memory leaked