javascript - 从另一个函数解析函数内的 promise

Question

我想从speak函数中解析updateGuider函数，如下所示:

tutor();

async function tutor(){
console.log('tutor function initiated..');
// wait until updateGuider function resolves
await updateGuider('default');
// The expected result is to reach this line after updateGuider resolves, but we can't so far!
console.log('Procccess Ends');


}
// Not working unless we use var instead of let?!
let updateGuiderResolve;

function updateGuider(state){    
  return new Promise((resolve) => { 
  updateGuiderResolve = resolve;
    switch(state) {
          case 'default':
          speak();
          break;         
    }
    
    });  
}


async function speak(){
   console.log('entered speak')
   setTimeout(function(){
     //after 5 seconds we resolve the updateGuider from speak function
     updateGuiderResolve();     
   },5000)
  
}  

如您所见，代码不起作用(预期结果是 5 秒后看到 console.log('Procccess Ends'))；

我注意到，如果我将 let updateGuiderResolve 更改为 var updateGuiderResolve 一切正常!为什么？

Answer 1

let 的问题是(正如错误消息所解释的那样)您是 trying to use the variable before it has been initialised :您正在 let updateGuiderResolve; 声明上方调用 tutor()。

但实际上，解析器函数根本不需要这个全局/静态共享变量。相反，让 speak 创建并返回 Promise 本身:

async function tutor() {
  console.log('tutor function initiated..');
  await updateGuider('default');
  console.log('Procccess Ends');
}

async function updateGuider(state) {
  switch(state) {
     case 'default':
       return speak();   
  }
}

function speak() {
  console.log('entered speak')
  return new Promise(function(resolve) {
    setTimeout(resolve, 5000);
  });
}

tutor().catch(console.error);