I am trying to understand async calls using async/await and try/catch.
In the example below, how can I save my successful response to a variable that can be utilized throughout the rest of the code?
const axios = require('axios');
const users = 'http://localhost:3000/users';
const asyncExample = async () =>{
try {
const data = await axios(users);
console.log(data); //200
}
catch (err) {
console.log(err);
}
};
//Save response on a variable
const globalData = asyncExample();
console.log(globalData) //Promise { <pending> }
1) Return something from your asyncExample function
const asyncExample = async () => {
const result = await axios(users)
return result
}
2) Call that function and handle its returned Promise:
;(async () => {
const users = await asyncExample()
console.log(users)
})()
Here's why should you handle it like this:
You can't do top-level await (there's a proposal for it though);
await must exist within an async function.
However I must point out that your original example doesn't need async/await
at all; Since axios already returns a Promise you can simply do:
const asyncExample = () => {
return axios(users)
}
const users = await asyncExample()
try..catch creates a new block scope. Use let to define data before try..catch instead of const, return data from asyncExample function call
(async() => {
const users = 123;
const asyncExample = async() => {
let data;
try {
data = await Promise.resolve(users);
} catch (err) {
console.log(err);
}
return data;
};
//Save response on a variable
const globalData = await asyncExample();
console.log(globalData);
// return globalData;
})();
I had same issue with you and found this post. After 2 days of trying I finally found a simple solution.
According to the document of JS, an async function will only return a Promise object instead of value. To access the response of Promise, you have to use .then()method or await which can return the resulting object of Promise is instead of Promise itself.
To change variables from await, you have access and change the variable you want to assign within the async function instead of return from it.
//Save response on a variable
var globalData;
const asyncExample = async () =>{
try {
const data = await axios(users);
globalData = data; // this will change globalData
console.log(data); //200
}
catch (err) {
console.log(err);
}
};
asyncExample();
But if you do this, you may get an undefined output.
asyncExample();
console.log(globalData) //undefined
Since asyncExample() is an async function, when console.log is called, asyncExample() has not finished yet, so globalData is still not assigned. The following code will call console.log after asyncExample() was done.
const show = async () => {
await asyncExample();
console.log(globalData);
}
show();
Because the events are happening asynchronously you need to tie in a callback/promise. I'm going to assume it returns a promise.
const axios = require('axios');
const users = 'http://localhost:3000/users';
const asyncExample = async () =>{
try {
const data = await axios(users);
console.log(data); //200
}
catch (err) {
console.log(err);
}
};
//Save response on a variable
const globalData = asyncExample().then( (success, err) => {
if (err) { console.error(err); }
console.log(success)
}
Just use a callback/promise (cascading programming):
axios(users).then(function(response) {
const globalData = response;
console.log(globalData)
});
Related
I want to wait on the HTTP POST request to complete and then return response to the caller function. I am getting Undefined when I print the received results.
I have defined post method as below:
// httpFile.js
const axios = require('axios');
module.exports = {
getPostResult: async function(params) {
console.log("getPostResult async called...");
var result = await axios.post("https://post.some.url", params)
.then ((response) => {
console.log("getPostResult async success");
return {response.data.param};
})
.catch ((error) => {
console.log("getPostResult async failed");
return {error.response.data.param};
});
}
}
And I am calling it in this way:
// someFile.js
const httpFile = require('./httpFile');
// Called on some ext. event
async function getPostResult() {
var params = {var: 1};
var result = await httpFile.getPostResult(params);
// Getting Undefined
console.log("Done Result: " + JSON.stringify(result));
}
I don't want to handle the .then and .catch in the calling function as I want to return the different values based on the POST result.
How should I wait for the response and get the return results.
In the above code I am getting the log statements as expected and "Done Result" get printed at the very end after the 'getPostResult' returns.
you are using both await & .then thats why it returns undefined.
this is how it should look
// httpFile.js
const axios = require('axios')
module.exports = {
getPostResult: async function (params) {
try {
const res = await axios.post('https://post.some.url', params)
return res.data
} catch (error) {
// I wouldn't recommend catching error,
// since there is no way to distinguish between response & error
return error.response.data
}
},
}
if you want to catch error outside of this function then this is way to go.
getPostResult: async function (params) {
const res = await axios.post('https://post.some.url', params)
return res.data
},
To make my code cleaner I want to use fetched API data in a few different functions, instead of one big. Even though I 've did manage to reffer to that data in other functions, the problem is the API im a fetching throws different, randomized results every time it is called. And so the output from userData() does not equal that from userData2(), even though my intention is different and I'd like the result variable contents to be the same between functions.
const getData = () =>
fetch("https://opentdb.com/api.php?amount=10").then((response) =>
response.json()
);
const useData = async () => {
const result = await getData();
console.log(result);
};
const useData2 = async () => {
const result = await getData();
console.log(result);
};
Your getData() function returns a promise. One fun fact about promises is that while they can only resolve once, that resolved value can be accessed and used as many times as you want.
const dataPromise = getData();
const useData = async () => {
const result = await dataPromise;
console.log(result);
};
const useData2 = async () => {
const result = await dataPromise;
console.log(result);
};
Using await resolves the promise value, the equivalent of...
dataPromise.then((result) => {
console.log(result);
});
// or `dataPromise.then(console.log)` if you like brevity
I like to point this out about the fetch-api... you should always check the Response.ok property
const getData = async () => {
const res = await fetch("https://opentdb.com/api.php?amount=10");
if (!res.ok) {
throw new Error(`${res.status}: ${await res.text()}`);
}
return res.json();
};
I'm using The Movie Database API. And the problem that i can't solve is returning "keys" variable when i call the function with Movie's id.I'm new on JavaScript that's why i can't solve this. Hope someone can help me, thanks in advance.
const APIURL = "https://api.themoviedb.org/3/discover/movie?sort_by=popularity.desc&api_key=[MY API KEY HERE]&page-1";
getMovies(APIURL)
async function getMovies(url)
{
const resp = await fetch(url);
const respData = await resp.json();
showMovies(respData.results)
}
async function getTrailer(id)
{
const resp = await fetch(`https://api.themoviedb.org/3/movie/${id}/videos?api_key=[MY API KEY HERE]&language=en-US`);
const respDataa = await resp.json();
let results = respDataa.results;
let keys = results[0].key;
return keys;
}
function showMovies(movies){
movies.forEach(movie => {
const modals = document.createElement('div');
modals.classList.add('modal');
modals.innerHTML = ` <a target="_blank" href ="https://www.youtube.com/watch?v=${getTrailer(movie.id)}">Watch Trailer</a>`
}
}
Well, first of all, always hide your api keys if you're posting your code somewhere (even if it's a private repository, you shouldn't do it).
Secondly, if you want to return multiple keys, you can map the results to extract id from each of them and do a return:
async function getTrailer(id)
{
const resp = await fetch(`https://api.themoviedb.org/3/movie/${id}/videos?api_key=04c35731a5ee918f014970082a0088b1&language=en-US`);
const respDataa = await resp.json();
let results = respDataa.results;
return results.map(({ key }) => key);
}
Async functions return a Promise in JavaScript.
Simply add return keys at the end of your function.
Then you can do:
getTrailer(528085).then(data => {
// do something with the data
})
You can also handle errors:
getTrailer(528085)
.then(data => {
// do something with the data
})
.catch(err => {
/*
An error occured. You can use err.toString() to convert the error into a string
*/
})
If you want to get the returned data immediately from an async function(or a promise), put your logic inside an async function, then you can simply do:
let keys = await getTrailer(528085)
And, here is how to handle errors in async/await:
try {
let keys = await getTrailer(528085)
}
catch(err){
/*
An error occured. You can use err.toString() to convert the error into a string
*/
}
By the way, like Desiigner said, don't keep your API keys in the client. Anyone can see your API key. Use a server to return the API response to the client.
We have to await or.then the return (it’s a Promise).
function showMovies(movies) {
// make the forEach callback async
movies.forEach(async (movie) => {
console.log(getTrailer(movie.id)) // Promise {<pending>}
const trailer = await getTrailer(movie.id);
console.log({ trailer });
const modals = document.createElement("div");
modals.classList.add("modal");
modals.innerHTML = ` <a target="_blank" href ="https://www.youtube.com/watch?v=${trailer}">Watch Trailer</a>`;
});
}
I am having a problem where an async function does not appear to be waiting. I am calling one async function from another, with the second returning a value after async operations have completed and then the first should be returning this as it has awaited it. But when logging accessToken in the first function it logs before awaiting the return from the second. Where am I going wrong? Thanks in advance.
export const confirmCode = async (verificationId, code) => {
try {
const credential = await firebase.auth.PhoneAuthProvider.credential(verificationId, code);
const accessToken = await authenticate(credential);
console.log(accessToken); // prints undefined as does not wait for above function call?
return accessToken;
} catch (error) {
console.log(error)
// this.showMessageErrorByCode(e.error.code);
}
}
const authenticate = async (credential) => {
try {
await firebase.auth().signInWithCredential(credential).then(result => {
const user = result.user;
user.getIdToken().then(accessToken => {
return accessToken;
});
})
} catch (error) {
console.log(error);
}
}
You should not mix async/await with the older version .then().
Just use it without then() like so:
export const confirmCode = async (verificationId, code) => {
try {
const credential = await firebase.auth.PhoneAuthProvider.credential(verificationId, code);
const accessToken = await authenticate(credential);
console.log(accessToken); // prints undefined as does not wait for above function call?
return accessToken;
} catch (error) {
console.log(error)
// this.showMessageErrorByCode(e.error.code);
}
}
const authenticate = async (credential) => {
try {
let result = await firebase.auth().signInWithCredential(credential); // <-- use await
const user = result.user;
accessToken = await user.getIdToken(); // <-- use await
return accessToken;
} catch (error) {
console.log(error);
}
}
For more detailed explanation, why your code does not work:
You are returning from within a .then() which is not possible
If you would want to use the old way of writing async functions, you would need to use:
return new Promise((resolve, reject) => { /* Code ... */ }); to wrap your function content
resolve(accessToken) instead of return
.then() and .catch() instead of await and try/catch
and some rejects where you can't resolve anything (so probably in the catch block)
But I would suggest you to use the async/await approach, as it is easier to read.
I started started a node environment based off express, my issue is more with Promise.
I've written a module that has an http call (axios) and i'm using async/await in order to receive the response and handle it, everything is working great in the module in terms of flow and i'm able to execute console.log()s, yet my returned value isn't coming back to index.js.
index.js
works great and my readFile() function works great.
const getDistance = require('./actions/getDistance');
app.post('/find-closest', async (req, res) =>{
try{
let address = req.body.address;
let data = await readFile('src/agents.json');
return res.json(getDistance(JSON.parse(data),address));
} catch (e) {
console.log('Error');
console.log(e);
return res.json(e);
}
});
getDistance.js
module.exports = function (agents, origins) {
let destinations = '&destinations=' + agents.map(agent => agent.address).join('|');
const getDistances = async () => {
try {
return await axios.get(url + origins + destinations + apiKey)
} catch (error) {
console.error(error)
}
};
const setDistancesResponse = async () => {
const distances = await getDistances()
console.log('test',distances.data); //<=this returns
return 'baboom'; //this is not returned through
};
setDistancesResponse();
};
I am expecting my endpoint to return a JSON response of the string "baboom".
What am I doing wrong here?
Thanks, Bud
Your exported getDistance function doesn't return anything. You are probably looking for
module.exports = async function(agents, origins) {
const destinations = '&destinations=' + agents.map(agent => agent.address).join('|');
const distances = await axios.get(url + origins + destinations + apiKey)
console.log('test',distances.data); // this logs something
return 'baboom';
};
and given that this now returns a promise, you will have to wait for the result value:
app.post('/find-closest', async (req, res) =>{
try{
let address = req.body.address;
let data = await readFile('src/agents.json');
return res.json(await getDistance(JSON.parse(data), address));
// ^^^^^
} catch (e) {
console.error('Error', e);
return res.json(e);
}
});
I think you misses return value. Try this:
return setDistancesResponse();