JS Promise 类似callback 实现 asynchronous

Promise

const posts=[
  {title:'Post One', body:"this is post one"},
  {title:'Post Two', body:"this is post two"}
]

function createPost(post){   //2秒后create post
  return new Promise(function(resolve,reject){
    setTimeout(function(){
      posts.push(post);
      const error = true;
      
      if(!error){
        resolve();  //成功的动作
      }else{
        reject(`Error: Something went wrong`);  //失败的动作
      }
    },2000);
  });
}

function getPosts(){
  setTimeout(function(){   //1秒后get post
    let output ="";
    posts.forEach(function(post){
      output+=`<li>${post.title}</li>`;
    });
    document.body.innerHTML=output;
  },1000);
}


createPost({title:'Post Three', body:"this is post three"})
.then(getPosts)
.catch(function(err){
  console.log(err);
});

Promise的function传入resolve和reject；
reject可被catch；
resolve可作为then之后的动作；