ES6Promise

一、常用方式

var state=false;

var p =new Promise((success,fail)=>{
    if(state){
        success("执行成功");
    }else{
        fail("执行失败");
    }
})

p.then(res=>{
    console.log(res);
}).catch(res=>{
    console.log(res);
})

var get_all_thing="";

function p1(){
    return new Promise(give_you_something=>{
        setTimeout(()=>{
            var time=new Date().getMinutes()+" : "+new Date().getSeconds()+"\n";
            give_you_something(time)
        },3000)
    })
}
function p2(){
    return new Promise(give_you_something=>{
        setTimeout(()=>{
            var time=new Date().getMinutes()+" : "+new Date().getSeconds()+"\n";
            give_you_something(time)
        },3000)
    })
}
function p3(){
    return new Promise(give_you_something=>{
        setTimeout(()=>{
            var time=new Date().getMinutes()+" : "+new Date().getSeconds()+"\n";
            give_you_something(time)
        },3000)
    })
}
function p4(){
    return new Promise(give_you_something=>{
        setTimeout(()=>{
            var time=new Date().getMinutes()+" : "+new Date().getSeconds()+"\n";
            give_you_something(time)
        },3000)
    })
}

p1().then(res=>{
    get_all_thing+=res;
    return p2();
}).then(res=>{
    get_all_thing+=res;
    return p3();
}).then(res=>{
    get_all_thing+=res;
    return p4();
}).then(res=>{
    get_all_thing+=res;
    console.log(get_all_thing);
})

function p1(arg){
    return new Promise(give_you_something=>{
        setTimeout(()=>{
            var time=new Date().getMinutes()+" : "+new Date().getSeconds()+"\n";
            arg+=time;
            give_you_something(arg)
        },3000)
    })
}
function p2(arg){
    return new Promise(give_you_something=>{
        setTimeout(()=>{
            var time=new Date().getMinutes()+" : "+new Date().getSeconds()+"\n";
            arg+=time;
            give_you_something(arg)
        },3000)
    })
}
function p3(arg){
    return new Promise(give_you_something=>{
        setTimeout(()=>{
            var time=new Date().getMinutes()+" : "+new Date().getSeconds()+"\n";
            arg+=time;
            give_you_something(arg)
        },3000)
    })
}
function p4(arg){
    return new Promise(give_you_something=>{
        setTimeout(()=>{
            var time=new Date().getMinutes()+" : "+new Date().getSeconds()+"\n";
            arg+=time;
            give_you_something(arg)
        },3000)
    })
}

p1("").then(res=>{
    return p2(res);
}).then(res=>{
    return p3(res);
}).then(res=>{
    return p4(res);
}).then(res=>{
    console.log(res);
})

二、then方法

// then()返回值仍为promise对象
let p1 = new Promise((success, fail) => {
  success(123)
}).then(res => {
  return 123
})

p1.then(res => {
  console.log(res)
  return new Promise((success, fail) => {
    success(456)
  })  // 等价于return 456
}).then(res => {
  console.log(res)
})