let arr = [1,2,3];
arr .reduce((promise,current)=>{
return promise.then(()=>{
return new Promise(resolve=>{
setTimeout(()=>{
console.log(current);
resolve()
},1000)
})
})
},Promise.resolve())
//总结：想要依次加载，上一个promise必须为完成状态，那么.then()里面的内容才可以继续执行，.then()之后的队列想要继续执行，那么当前.then()同样需要返回一个成功状态的promise
队列渲染示例：
let data = [
{
id:1,
name:'jay',
email:'jayking1314@126.com'
},
{
id:2,
name:'see',
email:'jayking1314@126.com'
}
]
function getUser(name){
return new Promise((resolve,reject)=>{
let theData = null;
for(v of data){
if(v.name === name){
theData = v;
break;
}
}
if(theData){
resolve(theData);
}
else{
reject('no data...')
}
})
}
class User{
constructor(name) {
this.name = name;
}
render(users){
users.reduce((promise,current)=>{
return promise.then(()=>{
return getUser(current).then(res=>{
return this.view(res);
})
})
},Promise.resolve())
}
view(user){
return new Promise(resolve=>{
setTimeout(()=>{
let h2 = document.createElement('h2');
h2.innerHTML = user.name;
document.body.appendChild(h2);
resolve();
},1000)
})
}
}
new User().render(['jay','see']);
