I've got some noob question I guess, but I can't undestand why this code not working as expected.
Problem is that I want to use result of my promise (array) to call ids that I need, but for some reason its not working as I expect. If I call b.then((customerIds) => customerIds) just after b, I got my array with values, but if I call it on body, its not working.
const a = fetch('/orders').then(rawOrders => rawOrders.json())
let b = a.then((orders) => {
let customersList = []
orders.forEach(element => {
customersList.push(element.customer)
});
return customersList
})
fetch('/users', {
method: 'POST',
headers: {
'Content-Type': 'application/json'
},
body: JSON.stringify({
ids: b.then((customerIds) => customerIds)
}) // Here is the problem
}).then(rawUsers => rawUsers.json()).then(users => console.log('users', users));
you can do the second fetch inside b.then callback
like:
const a = fetch('/orders').then(rawOrders => rawOrders.json())
let b = a.then((orders) => {
let customersList = []
orders.forEach(element => {
customersList.push(element.customer)
});
return customersList
});
b.then(customerIds =>fetch('/users', {
method: 'POST',
headers: {
'Content-Type': 'application/json'
},
body: JSON.stringify({
ids: customerIds
})
})).then(rawUsers => rawUsers.json()).then(users => console.log('users', users));
Although, I'd usually write that whole code block like
fetch('/orders')
.then(rawOrders => rawOrders.json())
.then(orders => orders.map(({customer}) => customer))
.then(ids => fetch('/users', {
method: 'POST',
headers: {
'Content-Type': 'application/json'
},
body: JSON.stringify({ids})
}))
.then(rawUsers => rawUsers.json())
.then(users => console.log('users', users))
.catch(err => console.error(err));
One long promise chain - with a catch at the end
Or async/await
(async () => {
try {
const rawOrders = await fetch('/orders');
const orders => await rawOrders.json();
const ids = orders.map(({customer}) => customer);
const rawUsers = await fetch('/users', {
method: 'POST',
headers: {
'Content-Type': 'application/json'
},
body: JSON.stringify({ids})
});
const users = await rawUsers.json();
console.log('users', users);
} catch(err) {
console.error(err);
}
})();
(the async IIFE is only needed if this code isn't inside an async function)
Related
I am trying to get pub locations data from MYSQL server and my fetch function works well. But after that, this try-catch block does not return anything. I also tried without try-catch block but it does not change anything
getPubsFromDatabase = async () => {
let response = await fetch(fetchDataUrl, {
method: 'POST',
headers:
{
'Accept': 'application/json',
'Content-Type': 'application/json',
},
});
try{
let json = await response.json();
console.log(json)
return json;
}
catch (error) {
console.log(error);
}
}
And here, I am trying to get the return value of the function. But in this version, I cannot even see any console.log output. What I mean by the version is, if I put 2nd line out of the async block without "await" keyword, I can see the console.log but I it gives "undefined" then.
(async () => {
const locationsData = await getPubsFromDatabase();
console.log(locationsData)
})()
You can use then and catch in the function fetch.
const getPubsFromDatabase = () => {
return fetch(fetchDataUrl, {
method: 'POST',
headers:
{
'Accept': 'application/json',
'Content-Type': 'application/json',
},
}).then(async (response) => {
const json = await response.json().then((data)=>{
return data;
}).catch((err)=>{
console.log('error from json method: ',err);
return { error: {
message: 'error from json method',
object: err
}};
});
console.log(json);
return json;
}).catch((error) => {
console.log('error from request: ', error);
return {
error: {
message: 'error from request', object: error
}
};
});
}
And when you use the method getPubsFromDatabase would be of the next way:
(async () => {
const locationsData = await getPubsFromDatabase();
console.log(locationsData);
})()
You can use Promise to return either result or error, In the example given below i have used axios library but you can also try same with fetch api
For Example
export const getData = () => {
return new Promise((resolve, reject) => {
const url = ApiConstant.BASE_URL + ApiConstant.ENDPOINT;
const API_HEADER = {
"Authorization": token,
};
axios
.get(url, {
headers: API_HEADER,
})
.then((res) => {
resolve(res.data);
})
.catch((error) => {
// handle error
reject(error);
console.log(error);
});
})
}
You can call the above function in component or screen like this:
getData().then(
(data) => {
}
).catch(
error => {
console.log(error)
}
)
I solved the problem by instead of returning the value from the function, I set the value inside the function. This seems to work now.
const [locationsData, setLocationsData] = useState();
getPubsFromDatabase = async () => {
let response = await fetch(fetchDataUrl, {
method: 'POST',
headers:
{
'Accept': 'application/json',
'Content-Type': 'application/json',
},
});
try{
let json = await response.json();
setLocationsData(json); // Here, I changed the value of the locationsData instead of returning
}
catch (error) {
console.log(error);
}
}
And to call the function:
useEffect(()=> {
getPubsFromDatabase();
},[])
I've been trying to make function(see bellow) to work. If i call this function in my test like this:
test.meta({ CID: 'C67', type: TestType.Critical }).timeouts({
pageLoadTimeout: 5000,})(
'Test to GetData',
async (t:TestController) => {
// When
const result = getData.getFinalData()
const finalResult = JSON.stringify(result)
console.log(finalResult)
})
In the log i get empty result:
Case Discovery
{}
But if i do console.log(data) inside the function, i do get the proper data.
So i just want to know how to get that data. As I will need later to use it for my test.
I was intending to use it like this:
const randomCaseId = finalResult[getRandomInt(1000)].caseId.toString()
public async getFinalData () {
fetch(TOKEN_API, {
method: 'post',
body: new URLSearchParams(details),
headers: { 'Content-Type': 'application/x-www-form-urlencoded' },
})
.then((res: { json: () => any; }) => res.json())
.then((json: any) => {
const token = (json.accessToken.toString())
console.log(token),
fetch(DATA_API, {
method: 'GET',
headers: { 'Content-Type': 'application/json' ,'authorization': `Bearer ${token}`}})
.then((res: { json: () => any; }) => res.json())
.then((json:any)=>{
const data = JSON.stringify(json)
return data;
}
)
})}
since getFinalData doesn't return anything, and it is async you'll never get anything but a promise that resolves to undefined when calling that function.
Why is getFinalData tagged async since you never use await. I would use async/await for simple code, rather than the .then chain you are using
To access the result of calling that function, you'll either need to await it, or use .then on the result - since the calling funciton is async, use await
Rewrite your code like
test.meta({ CID: 'C67', type: TestType.Critical })
.timeouts({pageLoadTimeout: 5000,})('Test to GetData', async (t:TestController) => {
// When
const finalResult = await getData.getFinalData();
console.log(finalResult)
})
and
public async getFinalData () {
const tokenres = await fetch(TOKEN_API, {
method: 'post',
body: new URLSearchParams(details),
headers: { 'Content-Type': 'application/x-www-form-urlencoded' },
});
const tokendata = await tokenres.json();
const token = tokendata.accessToken.toString();
console.log(token);
const res = await fetch(DATA_API, {
method: 'GET',
headers: { 'Content-Type': 'application/json' ,'authorization': `Bearer ${token}`}
});
// ** see note below, don't do the next two lines like this
const data = await res.json();
return data;
}
This code uses async/await properly, and doesn't stringify the data into JSON, twice!
Also, note
const data = await res.json();
return data;
can be the single line
return res.json();
Because that's how promises work
There are several problems here:
When you return a value inside the function which you've passed to then, it would not be returned as the value of the outer function
getFinalData is a async so it would return a promise
getFinalData is returning a promise but you never pass a value as the resolved data
You can use following code, which wait for the response:
test.meta({
CID: 'C67',
type: TestType.Critical
}).timeouts({
pageLoadTimeout: 5000,
})(
'Test to GetData',
async (t: TestController) => {
// When
const result = await getData.getFinalData()
const finalResult = JSON.stringify(result)
console.log(finalResult)
})
And also make sure to wait for the fetch and return the resolved value:
public async getFinalData() {
const res = await fetch(TOKEN_API, {
method: 'post',
body: new URLSearchParams(details),
headers: {
'Content-Type': 'application/x-www-form-urlencoded'
},
})
const json = await res.json();
const token = (json.accessToken.toString())
console.log(token);
const response = await fetch(DATA_API, {
method: 'GET',
headers: {
'Content-Type': 'application/json',
'authorization': `Bearer ${token}`
}
});
return response.json();
}
The below code always return the below wired object
{"_U": 0, "_V": 0, "_W": null, "_X": null}
as response.
Here is my code
getData = () => {
fetch('http://192.168.64.1:3000/getAll',{
method: 'GET',
headers: {
Accept: 'application/json',
'Content-Type': 'application/json'
}
})
.then((response) => {
console.log('Response:')
console.log(response.json())
console.info('=================================')
})
.catch(err => console.error(err));
}
componentDidMount(){
this.getData();
}
I am using node, express, Mysql as backend and react-native frontend
my backend code is here
app.get('/getAll',(req,res) => {
console.log('getAll method Called');
con.query('select * from dummy',(err,results,fields) => {
if(err) throw err;
console.log('Response');
console.log(results);
res.send(results);
});
});
The above code gives correct output in console but fetch API is not.
i cant find solution for the my problem. Thanks in advance.
That indicates that you are logging the promise before it resolves - the result of when you:
console.log(response.json())
How do I access promise callback value outside of the function?
As #Evert rightfully pointed out in comments, this is because response.json() returns a promise object.
So, you'll need to chain an additional .then() after you call response.json() where you log the resolved promise.
getData = () => {
fetch('http://192.168.64.1:3000/getAll',{
method: 'GET',
headers: {
Accept: 'application/json',
'Content-Type': 'application/json'
}
})
.then(response => response.json())
.then(data => {
console.log(data);
})
.catch(err => console.error(err));
}
Add async and await to your code:
getData = async () => {
await fetch('http://192.168.64.1:3000/getAll',{
method: 'GET',
headers: {
Accept: 'application/json',
'Content-Type': 'application/json'
}
})
.then((response) => {
console.log('Response:')
console.log(response.json())
console.info('=================================')
})
.catch(err => console.error(err));
}
So the issue is that you are not waiting for your Promise to resolve and this can be solved easily.
try {
const res = await fetch(
'your_api',
);
const data = await res.json();
} catch (error) {
console.log(error);
}
So the issue is that you are not waiting for your Promise to resolve. Have added await and that'll go next line once the await action is completed.
const user_fun = async (userId) => {
const response = await fetch("url");
const data = await response.json();
console.log("users ", data);
return data;
};
let data = user_fun();
console.log("users ", data);
const test = order.restaurantId;
console.log(test); //here test == 3
const getAvailableHours = async () =>{
console.log(test); //test == undefined
await fetch(`API Address`, {
method: 'POST',
headers: {
'Content-Type': 'application/x-www-form-urlencoded',
},
})
.then(response => {
return response.json();
})
.then(responseText => {
console.log(responseText);
})
.catch(error => {
console.log(error);
});
}
Hi, I am trying to fetch data from API by using restaurant ID but when I'm passing the ID to async it becomes undefined.
I am new in React.js, anyone has any ideas?
async await syntax allows you to avoid .then method, so you can handle promises with a more readable syntax. With try catch blocks you can handle errors, try this:
const getAvailableHours = async () => {
try {
let response = await fetch('https://api-address-goes-here/', {
method: 'POST',
headers: {
'Content-Type': 'application/x-www-form-urlencoded'
}
});
let responseText = await response.json();
return responseText;
} catch (err) {
console.log(err)
}
}
I have an arrow function which returns some data from an api call. i want to wrap it up inside a try catch block like
const fetchEmployees = () => (
try{
fetch('http://localhost:6873/api/values', {
method: 'GET',
headers: {
'content-type': 'application/json'
}
})
.then(response => response.json())
.then(names => { return names })
} catch (error) {
return error;
}
)
How could i do that? The perfectly working arrow function I have is
const fetchEmployees = () => (
fetch('http://localhost:6873/api/values', {
method: 'GET',
headers: {
'content-type': 'application/json'
}
})
.then(response => response.json())
.then(names => names )
)
You can't use try catch on fetch because fetch is async while try catch is sync. Therefore your try catch will always pass. if we assume that you received response, and .json() fails, in second then first parameter is success function second one is fail function that executes when .json() fails
const fetchEmployees = () => (
fetch('http://localhost:6873/api/values', {
method: 'GET',
headers: {
'content-type': 'application/json'
}
})
.then(response => response.json())
.then(names => names, error => "json failed" )
)
fetchEmployees().then(success => {}, error => {})
Like this when you call fetchEmployees in first function will be executed if everything succeed, otherwise second will execute with error response, in this case hard coded string "json failed"
Turn your function into an async one:
const fetchEmployees = async () => {
try {
const response = await fetch("http://localhost:6873/api/values", {
method: "GET",
headers: {
"content-type": "application/json"
}
});
const names = await response.json();
return names;
} catch (error) {
return error;
}
};
Try to use async/await
const fetchEmployees = async () => {
try {
let response = await fetch('http://localhost:6873/api/values', {
method: 'GET',
headers: {
'content-type': 'application/json'
}
});
let json = await response.json();
return json;
} catch (error) {
return error
}
}