一、常见的异步编程有

• 1、回调函数
• 2、promise
• 3、事件监听/发布订阅
• 4、rxjs

二、使用promise和rxjs实现异步编程的对比

• 1、使用promise异步编程的写法

  const promise = new Promise((resolve, reject) => {
    setTimeout(() => {
      resolve('promise成功了');
    }, 1000);
  });
  
  promise.then(data => {
    console.log(data);
  });
  

• 2、使用rxjs异步流编程的写法

  import { Observable } from 'rxjs';
  const stream = new Observable(observer => {
    setTimeout(() => {
      observer.next('rxjs成功了');
    });
  });
  stream.subscribe(data => {
    console.log(data);
  });
  

二、rxjs可以取消订阅,但是promise却不可以

• 1、具体实现代码

  import { Observable } from 'rxjs';
  
  const stream = new Observable(observer => {
    setTimeout(() => {
      observer.next('请求成功');
    }, 2000);
  });
  
  const disposable = stream.subscribe(data => {
    console.log(data);
  });
  
  setTimeout(() => {
    disposable.unsubscribe(); // 取消订阅
  }, 1000);
  

三、异步多次执行

对于promise的执行是一个状态到另外一个状态后是不可变的,结果要不是resole就是reject,但是不能回退

• 1、在promise中的定时器【只执行一次】

  const promise = new Promise((resolve, reject) => {
    setInterval(() => {
      resolve('promise成功了');
    }, 1000);
  });
  
  promise.then(data => {
    console.log(data);
  });
  

• 2、使用rxjs多次执行

  import { Observable } from 'rxjs';
  
  const stream = new Observable(observer => {
    let count: number = 0;
    setInterval(() => {
      observer.next(count++);
    }, 1000);
  });
  
  const disposable = stream.subscribe(data => {
    console.log(data);
  });
  

四、常见的操作符

• 1、使用方式

  import { Observable } from 'rxjs';
  import { map, filter } from 'rxjs/operators';
  
  const stream =
    new Observable() <
    number >
    (observer => {
      let count = 0;
      setInterval(() => {
        observer.next(count++);
      }, 1000);
    });
  
  stream
    .pipe(
      filter((x: number) => x % 2 === 0),
      map((x: number) => x * 2)
    )
    .subscribe(data => {
      console.log(data);
    });
  

• 2、常见的操作符见官网地址

  • Creation Operators创建异步流的操作符号
  • Join Creation Operators连接创建
  • Transformation Operators数据转换的
  • Filtering Operators过滤数据
  • Join Operators连接的操作符
  • Multicasting Operators
  • Error Handling Operators
  • Utility Operators
  • Conditional and Boolean Operators
  • Mathematical and Aggregate Operators

• 3、比如限制点击评率的过滤管道

  import { fromEvent } from 'rxjs';
  import { throttleTime } from 'rxjs/operators';
  
  const clicks = fromEvent(document, 'click');
  // 限制1000ms内不能重复点击
  const result = clicks.pipe(throttleTime(1000));
  result.subscribe(x => console.log(x));