异步等待无法正常工作

Question

I am new to JavasSript's async , await and promise features.

What I am doing is,

async function sendTextMessage(text) {
    console.log("----1----");
    var messageData = {
        message: {
            text: text
        }
    };
   await callSendAPI(messageData);
}

async function sendImageMessage(imageUrl) {
    console.log("----2----");
    var messageData = {
        message: {
            url: imageUrl
        }
    };
  await callSendAPI(messageData);
}

async function sendQuickReply(replies) {
    console.log("----3----");
    var messageData = {
        message: {
            text: text,
            quick_replies: replies
        }
    };
   await callSendAPI(messageData);
}
async function callSendAPI(messageData) {
    await request({
        uri: 'https://graph.facebook.com/v2.6/me/messages',
        qs: {
            access_token: config.FB_PAGE_TOKEN
        },
        method: 'POST',
        json: messageData

    }, function(error, response, body) {
        if (!error && response.statusCode == 200) {
            var recipientId = body.recipient_id;
            var messageId = body.message_id;

            if (messageId) {
                console.log("Successfully sent message with id %s to recipient %s",
                    messageId, recipientId);
            } else {
                console.log("Successfully called Send API for recipient %s",
                    recipientId);
            }
        } else {
            console.error("Failed calling Send API", response.statusCode, response.statusMessage, body.error);
        }
    });
}

I am calling this functions in one switch case like,

async function send(){
     await sendTextMessage(text);
     await sendImageMessage(img);
     await sendQuickReply(replies)  
}
send()

But while response shows sendImageMessage() last because this function may be not getting ready when I am sending imageUrl to generate a response.

Answer 1

Note this answer was written against the original question and not later edits made by the OP.

---

An async function is asynchronous. Other functions will not wait for it.

So you call sendTextMessage which calls callSendAPI and then the rest of the program carries on.

callSendAPI runs asynchronously. It calls request and waits for the promise returned by request to be resolved. When it has resolved, callSendAPI picks up the return value of request (well, it would if you captured the return value) and then continues with the next line (only there isn't a next line).

---

async / await do not make asynchronous code synchronous. They just make it look like it in inside the function declared as async which, itself, becomes asynchronous.

---

You could put your three function calls in an async function of their own, make sure each one returns a Promise, and then call each of those three with await .

---

See also How do I return the response from an asynchronous call? .

Answer 2

I hope that all you want todo is process some operations in strict order.

This is why async and await in ES6 exists.

So by example it may be like this do A then do B then do C or A > B > C

As you can see the last method do3 has only 500 ms delay but it is executed as last and not as first one. Without async and await operators it would be executed as first function and this is default behavior of JavaScript execution. Broser will execute sync code as first and async after. But not with async and await anymore :)

You should also know that if you prefix string, number of function with await then the will be transformed into promise automatically.

The console will print :

'juraj1'
'juraj2'
'juraj3'

here is simple example :

function do1() {
      return new Promise(resolve => {
          return setTimeout(() => resolve("juraj1"), 3000);
   });
 }
function do2() {
      return new Promise(resolve => {
            return setTimeout(() => resolve("juraj2"), 2000);
  });
 }

function do3() {
      return new Promise(resolve => {
             return setTimeout(() => resolve("juraj3"), 500);
  });
}

async function ForceAsynTOBeSync() {
    const a = await do1();

    console.log(a);

    const b = await do2();

    console.log(b);

    const c = await do3();

    console.log(c);
  }

  ForceAsynTOBeSync();

Answer 3

You have to await the API calls:

 await callSendAPI(messageData);

And therefore the functions these calls are in need to be async too and await ed when called and so on.