将下列异步函数改编成promise
<script>
function fn(resolve,reject){
setTimeout(function(){
console.log('3秒后执行')
},3000)
}
fn()
console.log('立即执行')
</script>
改编后的代码:
<script> let p = new Promise( function fn(resolve,reject){ setTimeout(function(){ resolve() },3000) } ) p.then(function(){ console.log('3秒后执行') }) console.log('立即执行') </script>