异步

1.事件实现异步

class Eventer {
  map = null;
  constructor() {
    this.map = {};
  }
  add(name, fn) {
    if (this.map[name]) {
      this.map[name].push(fn);
      return;
    }
    this.map[name] = [fn];
    return this; //返回实例,实现链式调用
  }
  emit(name, ...args) {
    this.map[name].forEach(fn => {
      fn(...args);
    });
    return this;
  }
}

let e = new Eventer();
e.add("hello", (err, name) => {
  if (err) {
    console.log(err);
    return;
  }
  console.log(name);
}).emit('hello', '发生了错误').emit('hello', null, "hello node.js");

2.观察者模式

function create(
  fn: (param: IObserverParam) => void
): (param: IObserverParam) => (param: IObserverParam) => void {
  let ret = false;
  return ({ next, complete, error }) => {
    function nextFn(...args) {
      if (ret) {
        return;
      }
      next(...args);
    }
    function completeFn(...args) {
      complete(...args);
      ret = true;
    }
    function errorFn(...args) {
      error(...args);
    }
    fn({ next: nextFn, complete: completeFn, error: errorFn });
    return () => (ret = true);
  };
}

interface IObserverParam {
  next: Function;
  complete: Function;
  error: Function;
}
let observer = create(observer => {
  setTimeout(() => {
    observer.next(1);
  }, 1000);
  observer.next(2);
  observer.complete(3);
});
const subject: IObserverParam = {
  next: value => {
    console.log(value);
  },
  complete: console.log,
  error: console.log
};

var unsubscribe = observer(subject);

3.promise异步

const getName = new Promise((resolve, reject) => {
  setTimeout(() => {
    resolve("nodejs");
  }, 1000);
});
getName.then(res => {
  console.log(res);
});
Promise.all([getName,getName]).then(console.log).catch(console.log);
Promise.race([getName,getName]).then(console.log).catch(console.log);

4.async/await

async function func(s: string) {
  return s;
}
// 或者
function func(s: string) {
  return Promise.resolve(s);
}
function log(res) {
  console.log(res);
  return res; // 继续返回promise
}
func("a")
  .then(log) // a
  .then(log) // a
  .then(log) // a
  .then(log); // a