I have the following promise function which uses fetch to get data from an API:
const getContacts = token =>
new Promise((resolve, reject) => {
fetch(url, {
method: 'GET',
headers: {
'Content-Type': 'application/json',
},
})
.then(response => response.json())
.then((data) => {
resolve(data);
})
.catch(err => reject(err));
});
This function is then called in a different file:
getContacts(token)
.then((data) => {
const contacts = data.data;
console.log(contacts);
})
.catch(err => console.error(err));
When there is a larger amount of data returned from the API, it is paginated. The response includes a link that needs to be fetched in order to get the next page. I want my code to first iterate through all pages and collect all data, then resolve the promise. When execution reaches the const contacts = data.data line, it should have data from every page (currently it returns only the first page).
What would be the best way to achieve this?
EDIT:
I tried recursion inside the getContacts function. This way I can iterate through all pages and get all data in one object, but I don't know what's the right way to resolve this back to the code, which initially called the function. The code below doesn't resolve correctly.
const getContacts = (token, allData, startFrom) =>
new Promise((resolve, reject) => {
if (startFrom) {
url = `${url}?${startFrom}`; // the api returns a set of results starting at startFrom (this is an id)
}
fetch(url, {
method: 'GET',
headers: {
'Content-Type': 'application/json',
},
})
.then(response => response.json())
.then((data) => {
let nextPageExists = false;
Object.assign(allData, data.data);
data.links.forEach((link) => {
if (link.rel === 'next') {
nextPageExists = true;
getContacts(token, allData, link.uri);
}
});
if (!nextPageExists) {
resolve({ data: allData });
}
})
.catch(err => reject(err));
});
I have the following promise function which uses fetch to get data from an API:
const getContacts = token =>
new Promise((resolve, reject) => {
fetch(url, {
method: 'GET',
headers: {
'Content-Type': 'application/json',
},
})
.then(response => response.json())
.then((data) => {
resolve(data);
})
.catch(err => reject(err));
});
This function is then called in a different file:
getContacts(token)
.then((data) => {
const contacts = data.data;
console.log(contacts);
})
.catch(err => console.error(err));
When there is a larger amount of data returned from the API, it is paginated. The response includes a link that needs to be fetched in order to get the next page. I want my code to first iterate through all pages and collect all data, then resolve the promise. When execution reaches the const contacts = data.data line, it should have data from every page (currently it returns only the first page).
What would be the best way to achieve this?
EDIT:
I tried recursion inside the getContacts function. This way I can iterate through all pages and get all data in one object, but I don't know what's the right way to resolve this back to the code, which initially called the function. The code below doesn't resolve correctly.
const getContacts = (token, allData, startFrom) =>
new Promise((resolve, reject) => {
if (startFrom) {
url = `${url}?${startFrom}`; // the api returns a set of results starting at startFrom (this is an id)
}
fetch(url, {
method: 'GET',
headers: {
'Content-Type': 'application/json',
},
})
.then(response => response.json())
.then((data) => {
let nextPageExists = false;
Object.assign(allData, data.data);
data.links.forEach((link) => {
if (link.rel === 'next') {
nextPageExists = true;
getContacts(token, allData, link.uri);
}
});
if (!nextPageExists) {
resolve({ data: allData });
}
})
.catch(err => reject(err));
});
-
Avoid the
Promiseconstructor antipattern! – Bergi Commented Jan 18, 2018 at 11:49 - How many rel=next links are there in a response? – Bergi Commented Jan 18, 2018 at 11:51
- There is just one rel=next link among a few other link types. – rok Commented Jan 18, 2018 at 12:15
2 Answers
Reset to default 7First of all, do not use the new Promise constructor when fetch already returns a promise.
Then, just use a recursive approach and chain your promises with then:
function getContacts(token, allData, startFrom) {
return fetch(startFrom ? url + '?' + startFrom : url, {
method: 'GET',
headers: {
'Content-Type': 'application/json',
},
}).then(response => response.json()).then(data => {
Object.assign(allData, data.data);
const nextPage = data.links.find(link => link.rel === 'next');
if (!nextPage)
return allData;
else
return getContacts(token, allData, nextPage.uri);
});
}
Here's a generic function using async/await syntax.
It returns itself until currentPage equals totalPages. You can retrieve these keys from your API response.
async function getData(perPage, page, options, allData = []) {
// fetch data
let base = 'https://api.example.';
let url = `${base}?perPage=${perPage}&page=${page}`;
let response = await fetch(url, options);
let data = await response.json();
// push this data object (or data.data... whatever) into allData array
allData.push(data);
// get 'totalPages' and 'currentPage' (or whatever your API names these)
let totalPages = data.pagination.total_pages;
let currentPage = data.pagination.current_page;
if (currentPage == totalPages) {
// you're done
return allData;
} else {
// get the next page and repeat
page++;
return getData(perPage, page, options, allData);
}
}
Calling it:
const options = {
method: 'GET',
headers: {
Accept: 'application/json',
appId: 'APP_ID',
apiKey: 'APP_KEY',
'Content-Type': 'application/json'
}
};
let perPage = 100;
let page = 1;
getData(perPage, page, options).then((data) => {
console.log(data)
}).catch((error) => {
console.log(error)
})