This question already has answers here:
How do I return the response from an asynchronous call?
(41 answers)
Closed 3 months ago.
I am trying to use a Node.JS application to make and receive API requests. It does a get request to another server using Axios with data it receives from an API call it receives. The second snippet is when the script returns the data from the call in. It will actually take it and write to the console, but it won't send it back in the second API.
function axiosTest() {
axios.get(url)
.then(function (response) {
console.log(response.data);
// I need this data here ^^
return response.data;
})
.catch(function (error) {
console.log(error);
});
}
...
axiosTestResult = axiosTest();
response.json({message: "Request received!", data: axiosTestResult});
I'm aware this is wrong, I'm just trying to find a way to make it work. The only way I can seem to get data out of it is through console.log, which isn't helpful in my situation.
The issue is that the original axiosTest() function isn't returning the promise. Here's an extended explanation for clarity:
function axiosTest() {
// create a promise for the axios request
const promise = axios.get(url)
// using .then, create a new promise which extracts the data
const dataPromise = promise.then((response) => response.data)
// return it
return dataPromise
}
// now we can use that data from the outside!
axiosTest()
.then(data => {
response.json({ message: 'Request received!', data })
})
.catch(err => console.log(err))
The function can be written more succinctly:
function axiosTest() {
return axios.get(url).then(response => response.data)
}
Or with async/await:
async function axiosTest() {
const response = await axios.get(url)
return response.data
}
Guide on using promises
Info on async functions
I know this post is old. But i have seen several attempts of guys trying to answer using async and await but getting it wrong. This should clear it up for any new references
UPDATE: May 2022
This answer is still having lots of interest and have updated it to use arrow functions
const axiosTest = async () {
try {
const {data:response} = await axios.get(url) //use data destructuring to get data from the promise object
return response
}
catch (error) {
console.log(error);
}
}
you can populate the data you want with a simple callback function,
let's say we have a list named lst that we want to populate,
we have a function that pupulates pupulates list,
const lst = [];
const populateData = (data) => {lst.push(data)}
now we can pass the callback function to the function which is making the axios call and we can pupulate the list when we get data from response.
now we make our function that makes the request and pass populateData as a callback function.
function axiosTest (populateData) {
axios.get(url)
.then(function(response){
populateData(response.data);
})
.catch(function(error){
console.log(error);
});
}
The axios library creates a Promise() object. Promise is a built-in object in JavaScript ES6. When this object is instantiated using the new keyword, it takes a function as an argument. This single function in turn takes two arguments, each of which are also functions — resolve and reject.
Promises execute the client side code and, due to cool Javascript asynchronous flow, could eventually resolve one or two things, that resolution (generally considered to be a semantically equivalent to a Promise's success), or that rejection (widely considered to be an erroneous resolution). For instance, we can hold a reference to some Promise object which comprises a function that will eventually return a response object (that would be contained in the Promise object). So one way we could use such a promise is wait for the promise to resolve to some kind of response.
You might raise we don't want to be waiting seconds or so for our API to return a call! We want our UI to be able to do things while waiting for the API response. Failing that we would have a very slow user interface. So how do we handle this problem?
Well a Promise is asynchronous. In a standard implementation of engines responsible for executing Javascript code (such as Node, or the common browser) it will resolve in another process while we don't know in advance what the result of the promise will be. A usual strategy is to then send our functions (i.e. a React setState function for a class) to the promise, resolved depending on some kind of condition (dependent on our choice of library). This will result in our local Javascript objects being updated based on promise resolution. So instead of getters and setters (in traditional OOP) you can think of functions that you might send to your asynchronous methods.
I'll use Fetch in this example so you can try to understand what's going on in the promise and see if you can replicate my ideas within your axios code. Fetch is basically similar to axios without the innate JSON conversion, and has a different flow for resolving promises (which you should refer to the axios documentation to learn).
GetCache.js
const base_endpoint = BaseEndpoint + "cache/";
// Default function is going to take a selection, date, and a callback to execute.
// We're going to call the base endpoint and selection string passed to the original function.
// This will make our endpoint.
export default (selection, date, callback) => {
fetch(base_endpoint + selection + "/" + date)
// If the response is not within a 500 (according to Fetch docs) our promise object
// will _eventually_ resolve to a response.
.then(res => {
// Lets check the status of the response to make sure it's good.
if (res.status >= 400 && res.status < 600) {
throw new Error("Bad response");
}
// Let's also check the headers to make sure that the server "reckons" its serving
//up json
if (!res.headers.get("content-type").includes("application/json")) {
throw new TypeError("Response not JSON");
}
return res.json();
})
// Fulfilling these conditions lets return the data. But how do we get it out of the promise?
.then(data => {
// Using the function we passed to our original function silly! Since we've error
// handled above, we're ready to pass the response data as a callback.
callback(data);
})
// Fetch's promise will throw an error by default if the webserver returns a 500
// response (as notified by the response code in the HTTP header).
.catch(err => console.error(err));
};
Now we've written our GetCache method, lets see what it looks like to update a React component's state as an example...
Some React Component.jsx
// Make sure you import GetCache from GetCache.js!
resolveData() {
const { mySelection, date } = this.state; // We could also use props or pass to the function to acquire our selection and date.
const setData = data => {
this.setState({
data: data,
loading: false
// We could set loading to true and display a wee spinner
// while waiting for our response data,
// or rely on the local state of data being null.
});
};
GetCache("mySelelection", date, setData);
}
Ultimately, you don't "return" data as such, I mean you can but it's more idiomatic to change your way of thinking... Now we are sending data to asynchronous methods.
Happy Coding!
axiosTest() needs to return axios.get, which in turn returns a Promise.
From there, then can be used to execute a function when said Promise resolves.
See Promise for more info.
Alternatively, await can be used from within the scope of some async function.
// Dummy Url.
const url = 'https://jsonplaceholder.typicode.com/posts/1'
// Axios Test.
const axiosTest = axios.get
// Axios Test Data.
axiosTest(url).then(function(axiosTestResult) {
console.log('response.JSON:', {
message: 'Request received',
data: axiosTestResult.data
})
})
<script src="https://cdnjs.cloudflare.com/ajax/libs/axios/0.18.0/axios.js"></script>
IMO extremely important rule of thumb for your client side js code is to keep separated the data handling and ui building logic into different funcs, which is also valid for axios data fetching ... in this way your control flow and error handlings will be much more simple and easier to manage, as it could be seen from this
ok fetch
and this
NOK fetch
<script src="https://unpkg.com/axios/dist/axios.min.js"></script>
<script>
function getUrlParams (){
var url_params = new URLSearchParams();
if( window.location.toString().indexOf("?") != -1) {
var href_part = window.location.search.split('?')[1]
href_part.replace(/([^=&]+)=([^&]*)/g,
function(m, key, value) {
var attr = decodeURIComponent(key)
var val = decodeURIComponent(value)
url_params.append(attr,val);
});
}
// for(var pair of url_params.entries()) { consolas.log(pair[0]+ '->'+ pair[1]); }
return url_params ;
}
function getServerData (url, urlParams ){
if ( typeof url_params == "undefined" ) { urlParams = getUrlParams() }
return axios.get(url , { params: urlParams } )
.then(response => {
return response ;
})
.catch(function(error) {
console.error ( error )
return error.response;
})
}
// Action !!!
getServerData(url , url_params)
.then( response => {
if ( response.status === 204 ) {
var warningMsg = response.statusText
console.warn ( warningMsg )
return
} else if ( response.status === 404 || response.status === 400) {
var errorMsg = response.statusText // + ": " + response.data.msg // this is my api
console.error( errorMsg )
return ;
} else {
var data = response.data
var dataType = (typeof data)
if ( dataType === 'undefined' ) {
var msg = 'unexpected error occurred while fetching data !!!'
// pass here to the ui change method the msg aka
// showMyMsg ( msg , "error")
} else {
var items = data.dat // obs this is my api aka "dat" attribute - that is whatever happens to be your json key to get the data from
// call here the ui building method
// BuildList ( items )
}
return
}
})
</script>
After 6 hours of fluttering, I realized it was a one-line problem. If you are interfering with the axios life-cycle, you may have forgotten this line:
componentDidMount() {
this.requestInterceptor = axios.interceptors.request.use((request) => {
this.updateApiCallFor(request.url, true);
return request;
});
this.responseInterceptor = axios.interceptors.response.use((response) => {
this.updateApiCallFor(response.config.url, false);
return response; // THIS LINE IS IMPORTANT !
}, (error) => {
this.updateApiCallFor(error.config.url, false);
throw error;
});
async makes a function return a Promise
await makes a function wait for a Promise
code async/await
// https://www.npmjs.com/package/axios
const axios = require('axios')
/* --- */
async function axiosTest() {
let promiseAxios = axios.get( 'https://example.com' )
/* --- */
console.log( await promiseAxios )
}
/* --- */
axiosTest()
replit.com Stackoverflow - Returning data from Axios API
replit.com Stackoverflow - How to return values from async
code async/await with return
// https://www.npmjs.com/package/axios
const axios = require('axios')
/* --- */
async function axiosTest() {
console.log( await promiseAxios() )
}
/* --- */
axiosTest()
/* --- */
// create function for promise axios and return it
function promiseAxios() {
return axios.get( 'https://example.com' )
}
replit.com Stackoverflow - Returning data from Axios API - return
replit.com Stackoverflow - How to return values from async - return
Try this,
function axiosTest() {
axios.get(url)
.then(response => response.data)
.catch(error => error);
}
async function getResponse () {
const response = await axiosTest();
console.log(response);
}
getResponse()
It works, but each function where you want to get the response needs to be an async function or use an additional .then() callback.
function axiosTest() {
axios.get(url)
.then(response => response.data)
.catch(error => error);
}
async function getResponse () {
axiosTest().then(response => {
console.log(response)
});
}
getResponse()
If anyone knows a way to avoid this please do tell.
Also checkout Katsiaryna (Kate) Lupachova's article on Dev.to. I think it will help.
async handleResponse(){
const result = await this.axiosTest();
}
async axiosTest () {
return await axios.get(url)
.then(function (response) {
console.log(response.data);
return response.data;})
.catch(function (error) {
console.log(error);
});
}
You can find check https://flaviocopes.com/axios/#post-requests url and find some relevant information in the GET section of this post.
You can use Async - Await:
async function axiosTest() {
const response = await axios.get(url);
const data = await response.json();
}
Related
This question already has answers here:
Async function returning promise, instead of value
(3 answers)
How do I return the response from an asynchronous call?
(41 answers)
Closed 2 years ago.
I have 2 files in javascript.
One:
main_app.js
import * as API from "./api.js";
const pin = API.getPin();
console.log(pin);
other is api.js
const baseUrl = "https://some.com/api";
export function getPin() {
try {
axios.post(baseUrl, { method: "pin" }).then((res) => console.log(res));
} catch {
console.log("Fail");
}
}
In the first file I need to save the output of the getPin() but I always get Promise - pending in the console.
In the axios call and .then method I can console.log the correct data but whatever I try I am not able to return the data.
I have also tried async and await with no avail.
export async function getPin() {
try {
const res = await axios.post(baseUrl, { method: "pin" }).then(res => res.data);
return res.data;
} catch {
console.log("Fail");
}
}
I have tried class from es6 but with the same result and then thought I am probably not using the class correctly:
export class Api {
static baseUrl = "https://some.com/api";
static response = null;
static getPin() {
const body = { method: "pin" };
axios
.post(this.baseUrl, body)
.then((res) => (this.response = res.data))
.catch((err) => console.error(err));
}
}
I ve look at many articles and I am sure I am missing something obvious but I am losing my mind :-(
Any help would be appreciated
EDIT: Not really a duplicate with suggested question.I have re-did the class and it looks like this
export default class API {
static baseUrl = "https://some.com/api";
static response = null;
static pin = null;
static getPin() {
axios
.post(this.baseUrl, { method: "pin" })
.then((res) => (this.pin = res.data.pin));
return this.pin;
}
}
but this will STILL not working as I need.Help please
When using the async/await pattern with axios, .then is not needed. The await axios.post pauses the execution of code until the promise is resolved and returns the data from the API call, and thus allows for res.data to contain the response from the API. See below for a modified version of one of your examples:
export async function getPin() {
try {
// instead of this line:
// const res = await axios.post(baseUrl, { method: "pin" }).then(res => res.data);
// try the following, notice the .then() removed
const res = await axios.post(baseUrl, { method: "pin" });
// res contains the response from the API call, no need to use .then.
// you may want to console.log(res.data) out here instead to see what you get back first.
return res.data;
} catch(e) {
console.log("error: ", e);
}
}
In your main_app.js, you need to modify your code because API.getPin() is an asynchronous API call, that's why you're getting a promise.
import * as API from "./api.js";
let pinGlobal;
async function callAPIandSetPin() {
// must be awaited because API.getPin() is asynchronous.
const pin = await API.getPin();
console.log(pin);
// if you needed a global pin for whatever reason, you can modify it from here.
pinGlobal = pin;
}
callAPIandSetPin();
I'm trying to understand how to chain two different API calls including one with a for loop in a 'notes' Vue component. I have a really basic experience of promises and I'm looking to improve.
I'm making a first API call to get all the notes and pushing them into an array using a Vuex mutation. During that first API call I'm also mapping the different users emails into an Object.
Using this mapped object, I'm making a second API call inside a for loop to get all the users avatars.
Here's what the first API call looks like :
getAllNotesAPI(entity) {
noteService.getNotes(entity)
.then((response) => {
if (response.data.length === '0') {
// Set hasData to false if the response is 0
this.hasData = false;
} else {
// Push data into the note array using a store mutation
this.setAllNotes(response.data);
}
// Mapping all users emails into 'userEmails'
this.userEmails = [...new Set(response.data.map(x => x.userEmail))];
// Calling my second API call here to get all the avatars associated with these emails
for (let i = 0; i < this.userEmails.length; i++) {
this.getAvatarAPI(this.userEmails[i])
}
})
.catch((error) => {
console.log(error);
})
.finally(() => {
this.endLoader('notes');
});
},
this.getAvatarAPI is the second API call which looks like this :
getAvatarAPI(login) {
userService.getAvatar(login)
.then((response) => {
let newAvatar = {
userEmail: login,
picture: response.data.picture
};
// Push the response into a userAvatar Object using a store mutation
this.setUserAvatar(newAvatar);
}).catch((error) => {
console.log(error)
})
},
I've tried using async / await but couldn't figure out how to bind this inside of an async function (this.getAvatarAPI(this.userEmails)) was undefined, I've tried chaining using multiples then but couldn't figure out how to : get all my notes then all my avatars then end the 'note' loader once both those API calls are done.
If any of you could give me some pointers or the beginning of an answer that would be truly appreciated !
First whilst not related to your problem, avoid for loop when non necessary:
Do you need the i index?
for (let i = 0; i < this.userEmails.length; i++) {
this.getAvatarAPI(this.userEmails[i])
}
no. You need the userMail. Then
this.userEmails.forEach(userMail => {
this.getAvatarAPI(userEmail)
})
Now, to synchronize promises, you need to return a promise (let's not talk about async yet)
make getAvatarAPI return a promise
getAvatarAPI(login) {
return userService.getAvatar(login).then(blabla) // notice the return here
retrieve the promises of getAvatar API
let promises = this.userEmails.map(userMail => {
return getAvatarAPI(userEmail)
})
return after all promises have fulfilled
let promises = this.userEmails.map(userMail => {
return getAvatarAPI(userEmail)
})
return Promise.all(promises)
On a side note with async/await
If you use it you are not forced anymore to write return, you need to write async/await though
The underlying idea stay the same. Specifying the async keywords says that your function will return a promise-like.
e.g
async function p () {
return 5
}
p.then(x => console.log(x)) // does print 5 even though we didn't explicitely write return Promise.resolve(5)
Now you have to ensure you await the async function when you call it:
getAvatarAPI: async login => {
return userService.getAvatar(login).then(blabla)
}
// DO NOT do it
this.userEmails.forEach(userMail => {
return await this.getAvatarAPI(userEmail)
})
In forEach loop above, you will do your getAvatarAPI call in sequence because await "stops" iterating as long as getAvatarAPI has not resolved.
The proper way would be
getAllNotesAPI: async entity => {
try { // notice the necesary try-catch block
const response = await noteService.getNotes(entity)
blabla
let promises = this.userEmails.map(userMail => {
return this.getA...
})
let result = await Promise.all(promises)
// eventually return result, or simply await Promise... without lefthand-side assignment
} catch (error) {
console.log(error);
}
console.log(this.end('loader'))
}
I´m pretty new to Promises and found many examples here how to access the actual value which is always done with console.log. But my goal is to store the result in a variable and work with it.
getdata = () =>
fetch(
"https://www.alphavantage.co/query?function=TIME_SERIES_DAILY&symbol=MSFT&outputsize=full&apikey=demo"
)
.then(response => {
if (response.status === 200) {
return response.json();
} else {
throw new Error("This is an error");
}
})
.then(data => {
console.log(data);
});
getdata();
This code works. Can you help me to rewrite it that the getdata() function allows me to store the result in a variable. Return does not work since I will receive another pending Promise.
You can do it like this:
getdata = () =>
fetch(
"https://www.alphavantage.co/query?function=TIME_SERIES_DAILY&symbol=MSFT&outputsize=full&apikey=demo"
).then(response => {
if (response.status === 200) {
return response.json();
} else {
throw new Error("This is an error");
}
});
getdata().then(data => {
//I can do whatever with data
});
Of course you would also want to handle the scenario where the request failed, so you could also chain a .catch(). Alternately, if you have your build process configured for it, you can use async and await so you could do:
try {
const data = await getdata();
} catch(err) {
}
This would need to be in a function marked as async
Well at first we need to declare a variable let's say temp. Then use fetch API to request our query with URL. If server status is 200 then it will return a promise, we need to use then method by passing any argument (res, response, r anything...) and then a fat arrow function (=>) so that we can make the response as json format. After then we need to use another then method to return the json output and assign the value to our declared temp variable.
But if there is any error like 500, 400, 404 server error we need to use catch method with err argument and console it out.
let temp;
fetch('https://www.alphavantage.co/query?function=TIME_SERIES_DAILY&symbol=MSFT&outputsize=full&apikey=demo')
.then(res => res.json())
.then(data => temp = data)
.catch(err => console.log(err));
I appreciate that there are many questions on this but I can't seem to find a relevant answer.
I am using a Meteor call with a callback to a method on the server that shrinks an URL via bitly, but although this runs on the server, I am getting a undefined response back on the client.
Any ideas here is the code?
Client
Meteor.call('bitlyShrink','http://test.com', function(error, response) {
console.log(error);
console.log(response);
})
Server
Meteor.methods({
bitlyShrink(longurl) {
check (longurl, String);
const BitlyClient = require('bitly'),
bitly = BitlyClient('token');
bitly.shorten( longurl )
.then( function ( response ) {
console.log(response);
return response;
})
.catch( (error ) => {
return error;
});
}
});
That's a common mistake made while using Promises in Meteor methods.
To make Meteor resolve a Promise and return result to a client you should return the Promise at the end of this method:
Meteor.methods({
bitlyShrink(longurl) {
check (longurl, String);
const BitlyClient = require('bitly'),
bitly = BitlyClient('token');
const bitlyPromise = bitly.shorten(longurl);
// do something else, if needed
return bitlyPromise;
}
});
You should not add .catch(), it will be added by Meteor automatically.
Useful article to read: Using Promises and async/await in Meteor.
Maybe a trivial one, but I am new with Typescript and fetch API.
In an exported class I have a public method remoteFetchSomething like:
export class className {
remoteFetchSomething = (url : string) : Promise<Response> => {
return fetch(url)
.then(
(r) => r.json()
)
.catch((e) => {
console.log("API errore fetching " + objectType);
});
}
}
export const classInstance = new className();
The method queries a remote JSON API service, and in the code, I am using it like:
import { classInstance } from ...
classInstance.remoteFetchSomething('https://example.url')
.then((json) => {
console.log(json);
}
)
The console.log is actually showing the results, but the remoteFetchSomething returns a Promise and I am unable to parse and access the JSON object values.
I would like to wait for the response before executing the remaining code, but how do I unwrap content from promise? Should I again put another .then? What am I missing?
Thank you.
By now I resolved the problem defining the return type of the remoteFetch as any:
remoteFetchSomething = (url : string) : any => {
return fetch(url)
.then(
(r) => r.json()
)
.catch((e) => {
console.log("API errore fetching " + objectType);
});
}
And now I can access JSON values like data below:
classInstance.remoteFetchSomething('https://example.url').then(
(json) => {
console.dump(json.data);
}
)
[sincerely still not clear why I cant' use the Promise<Response> type]
You can't synchronously block while waiting for a request in javascript, it would lock up the user's interface!
In regular javascript, and most versions of TypeScript, you should be / must be returning a promise.
function doRequestNormal(): Promise<any> {
return fetch(...).then(...);
}
function someOtherMethodNormal() {
// do some code here
doRequestNormal.then(() => {
// continue your execution here after the request
});
}
In newer versions of typescript, there's async/await keyword support - so instead it might look like this:
async function doRequestAsync() {
var result = await fetch(...);
// do something with request;
return result;
}
async function someOtherMethodAsync() {
// do some code here
var json = await doRequestAsync();
// continue some code here
}
Keep in mind, doRequestAsync still returns a Promise under the hood - but when you call it, you can use await to pretend that you're blocking on it instead of needing to use the .then( callback. If you call an async method from a non-async method, you'll still need to use the callbacks as normal.
this is how I do it:
type Payload = {
id: number
}
type ReturnType = number
export const functionThatHasNumberType = async (
payload: Payload
): Promise<ReturnType> => {
let url = `/api/${payload.id}`
return await axios.get(url)
}