issue with promise Node.js

Question

I have been trying to figure this out for quite some time and it's too confusing so i thought i'd ask.

 var listenKey = ""; const createListenKey = async () => { await axios({ url: "/api/v3/userDataStream", method: "POST", baseURL: "https://api.binance.com", headers: { "X-MBX-APIKEY": "H48w9CLuTtTi955qWjcjjEKhh0Ogb3jnnluYucXXXXXXXXXXXXXXXX", }, }).then((response) => { var key = response.data.listenKey; console.log(key, "created"); return key; }); }; listenKey = createListenKey(); listenKey.then((key) => { console.log(key); });

the console.log in the last but one line is printing undefined. Why is that?

Thanks in advance!

Answer 1

You did not return anything from the async function createListenKey

const asynF = async ()=>{


Promise.resolve(1).then(res=>{

 //Simulating response from axios call
 console.log(res)
})

// you are not returning anyting from this function  equivalent of => return ;
}

asynF().then(res=>{
//this would log undefined 
console.log(res)
})

As you know async function returns a promise you have two options make the outer wrapper a async function as well and just use await like below

const key = await createListenKey(config)

or else

you could simply do this

   return createListenKey(config).then(res=>{

 listenKey = res
})

can't say much more without knowing context. Might I suggest not to mix then and async wait together

Answer 2

Because the createListenKey() function doesn't return anything. The return statement in the then clause inside that function is scoped in the then block. To return a value from an async function, you need to do something like this.

const createListenKey = async () => {
  const response = await axios({
    url: "/api/v3/userDataStream",
    method: "POST",
    baseURL: "https://api.binance.com",
    headers: {
      "X-MBX-APIKEY":
        "H48w9CLuTtTi955qWjcjjEKhh0Ogb3jnnluYucXXXXXXXXXXXXXXXX",
    },
  })

  var key = response.data.listenKey;
  console.log(key, "created");
  return key;
};