Promise本质:
1.等待异步操作结束
2.使用
1.let p=new Promimse((resolve,reject)=>{
//...省略了好多代码
//成功了,执行resolve()
//失败了,执行reject()
})
2.Promise.all([p1,p2,p3,...]).then(allResult=>{
},error=>{
});
3.Promise.race([p1,p2,p3,...]).then(allResult=>{
},error=>{
});