什么是RxJS？
Reactive Extension JavaScript. It's a reactive streams library that allows you to work with asynchronous data streams.
We represent asynchronous data streams using observable sequences.什么是asynchronous data streams?
1. asynchronous: When we called a function and want to be notified when the result is available, we will have to register a callback. In this way, we can continue with execution without worrying about the webpage becoming unresponsive.
2. data: Raw information in JavaScript.
3. streams: Sequences of data, in other words, information made available over time. Different from arrays, it doesn't have to be present in order.
何谓observable sequences?
就是observables。Observables are flexible and have to patterns: push and pull.
push pattern: We use the push pattern to subscribe to the source stream and react to new data.
pull pattern: We use the pull pattern in the same way above but, synchronously.