将 async-await 与 node-fetch 结合使用不会将响应返回给调用方法

Question

I have a function defined in a module that is supposed to do a fetch and return the response. I am having trouble returning the response from the fetch. The calling function gets the return value as "undefined".

I am new to JavaScript and Node so might need a little bit of hand-holding if you don't mind.

Calling function

async function executeTest() {
    try {
        const response = await bpc.postLendingApplication(
            blendConnection,
            loanData
        );
        console.log("Response from POST Loan: ", response);
    } catch (error) {
        console.log(error);
    }
}

Module function doing the fetch request

const fetch = require("node-fetch");
async function postLendingApplication(connection, data) {
    console.log("Processing POST Loan.");
    await fetch(connection.url, {
        method: "POST",
        headers: connection.headers,
        body: data,
    }).then(async res => {
        console.log("Status: ", res.status);
        console.log("StatusText: ", res.statusText);
        console.log("OK: ", res.ok);
        return await res;
    });
}

The console output is:

Processing POST Loan.
Status:  200
StatusText:  OK
OK:  true
Response from POST Loan:  undefined

As you can see, the fetch did what it was supposed to do and if I log the res.json() within the module method, it prints the payload. But I would like to return the error and response from the fetch so the module behaves as a generic method and the processing and error handling is done in the calling method.

Answer 1

When you mark a function as async , JavaScript will always return a Promise , thus making it asynchronous. When you return a value, it is resolving the Promise . Using await inside of these functions "pauses" execution (it is technically creating a new function for code that occurs after the await ) until the awaited Promise is resolved, standing in place of the usage of then(callback) . As such, you don't need then inside of any async function .

You do, however, need to treat your own async function as a Promise .

const fetch = require("node-fetch");
async function postLendingApplication(connection, data) {
    try {
      console.log("Processing POST Loan.");

      // the await eliminates the need for .then
      const res = await fetch(connection.url, {
          method: "POST",
          headers: connection.headers,
          body: data,
      })
      // this code is resumed once the fetch Promise is resolved.
      // res now has a value.
      console.log("Status: ", res.status);
      console.log("StatusText: ", res.statusText);
      return res;
   }
   catch(err) { 
     // because the promise could error, it is advised to use
     // try/catch. With a Promise, you would .then(cb).catch(errHandler)
     // but async/await doesn't utilize callbacks.

     // perform error handling or you can bubble it up.
    throw err
}

When calling postLendingApplication(connection, data) make sure that you are either using await , if inside an async function or postLendingApplication(connection, data).then(callback) as the return value will be a Promise .

postLendingApplication(connection, data).then(callback).catch(errHandler)

Answer 2

You forget to return form function. return await fetch(connection.url, { You dont need async-await in then function. You can return res.json()

const fetch = require("node-fetch");
async function postLendingApplication(connection, data) {
    console.log("Processing POST Loan.");
    return await fetch(connection.url, {
        method: "POST",
        headers: connection.headers,
        body: data,
    }).then(res => {
        console.log("Status: ", res.status);
        console.log("StatusText: ", res.statusText);
        console.log("OK: ", res.ok);
        return res.json();
    });
}