在 es6 中，将带有回调的事件侦听器变成可迭代的

Question

我的 websocket 类Wws使用onmessage侦听所有传入消息。

对于使用Wws程序，我的 websocket 模块，我希望它们通过iterable s“监听”。

例如，

// listen for new blog messages
let itr = ws.listen( 'blog', 'new' );

// display each new blog as we receive it
while( true ) {
  let blog = itr.next().value;
  dispBlog( blog );
}

任何数量的iterable可能挂在事件侦听器上。

你会如何在ws模块中编写generator ？

ws = function() {
  conn = new Websocket(...);

  // could have global `onmessage` that passes through the messages
  conn.onmessage = function(msg) {
    // can look at listeners and know there are iterators
    // but how to talk to them?
  }
  listeners = new Map();

  // generator for listening to incoming messages
  listener = function*( service, action ) {
    // can add this service.action to listeners, but what?
    // does this guy create his own `onmessage`?
    // if so, how does he get the `yield` to the outer function?
  }

如何将带有callback的listener iterator转换为iterator ？

Answer 1

您可以通过以下示例类以一种hacky 方式完成此操作：

export class WebSocketMessageGenerator {
    private receivedMessages: Data[] = [];
    constructor(private readonly client: WebSocket) {}

    public async * messages() {
        this.client.on("message", (data: Data) => {
            this.receivedMessages.push(data);
        });

        while (true) {
            if (this.receivedMessages.length > 0) {
                yield this.receivedMessages.shift();
                continue;
            }
            await new Promise((resolve) => setTimeout(resolve, 10));
        }
    }
}

像这样调用：

const generator = new WebSocketMessageGenerator(new Websocket("url"));
const data = (await generator.messages().next()).value;

我不确定如何避免 while 循环中的睡眠，但您可以将其调整为合理的值。