1-1 promise和定时器执行顺序

promise 会优先于 定时器

console.log("3");
setTimeout(()=>{
  console.log("2");
})
Promise.resolve().then(()=>{
  console.log("1");
})
/*
3
1
2
*/

1-2 await

await 阻塞线程 会从异步函数中跳出来，优先执行同步的代码

async function show(){
  console.log(1);
  var res = await 100;
  console.log(res);
}
show()
console.log(2);   // 1 2 100
setTimeout(()=>{
  console.log(3);
},1000)
/* 
 1
 2
 100
 3
*/

async function show(){
  console.log("script-start");
  var res = await go()
  console.log(res);
}
async function go(){
  return 1
}
show()
setTimeout(()=>{
  console.log(4);
},1000)
var p = new Promise((resolve,reject)=>{
  console.log(2);
  resolve(3)
})
p.then((res)=>{
  console.log(res);
})
console.log("script-start");
/* 
 script-start
 2
 script-start
 1
 3
 4
*/