JS es6 如何将两个请求写回调？

Question

有A、B两个promise请求，希望B在A返回结果后才发起，但又不想将B写到A里面去，请问怎么写？

Answer 1

functionA(){
returnnewPromise((res,rej)=>{
setTimeout(()=>{
console.log('A')
res('sayhifromA')
},1000)
})
}
functionB(data){
returnnewPromise((res,rej)=>{
setTimeout(()=>{
console.log('B')
console.log(data)
res()
},1000)
})
}
A().then(data=>B(data))
                            

Answer 2

functionresolveAfter2Seconds(x){
returnnewPromise(resolve=>{
setTimeout(()=>{
resolve(x);
},2000);
});
}
asyncfunctionadd2(x){
vara=awaitresolveAfter2Seconds(20);
varb=awaitresolveAfter2Seconds(30);
returnx+a+b;
}
add2(10).then(v=>{
console.log(v);//prints60after4seconds.
});