I was contacted by a Facebook recruiter on LinkedIn about a position of Frontend Developer based in London. Then we had a 15-minute call about background and simple technical questions, i.e., what are the differences between a queue and a stack, what is event propagation, what is the time complexity to traverse a balanced binary tree, etc. After that, in a week, I had a 45-minute call through BlueJeans and CoderPad whiteboard.

Write an emitter class:

javascript emitter = new Emitter();

// 1. Support subscribing to events. const sub = emitter.subscribe('event_name', callback); const sub2 = emitter.subscribe('event_name', callback2);

// 2. Support emitting events. // This particular example should lead to the callback above being invoked with foo and bar as parameters. emitter.emit('event_name', foo, bar);

// 3. Support unsubscribing existing subscriptions by releasing them. sub.release(); // sub is the reference returned by subscribe above

Given two identical DOM trees (not the same one), find the node in the other one from a given node.

Implement a simple store class with set(Node, value), get(Node), and has(Node) methods, which store a given Node with its corresponding value.