Firebase cloud function: http function returns null - node.js

Question

Here is what I am trying to do.
I am introducing functionality to enable users to search for local restaurants.
I created a HTTP cloud function, so that when the client delivers a keyword, the function will call an external API to search for the keyword, fetch the responses, and deliver the results.
In doing #2, I need to make two separate url requests and merge the results.
When I checked, the function does call the API, fetch the results and merge them without any issue. However, for some reason, it only returns null to the client.
Below is the code: could someone take a look and advise me on where I went wrong?
exports.restaurantSearch = functions.https.onCall((data,context)=>{
const request = data.request;
const k = encodeURIComponent(request);
const url1 = "an_url_to_call_the_external_API"+k;
const url2 = "another_url_to_call_the_external_API"+k;
const url_array = [ url1, url2 ];
const result_array = [];
const info_array = [];
url_array.forEach(url=>{
return fetch(url, {headers: {"Authorization": "API_KEY"}})
.then(response=>{
return response.json()
})
.then(res=>{
result_array.push(res.documents);
if (result_array.length===2) {
const new_result_array_2 = [...new Set((result_array))];
new_result_array_2.forEach(nra=>{
info_array.push([nra.place_name,nra.address_name])
})
//info_array is not null at this point, but the below code only return null when checked from the client
return info_array;
}
})
.catch(error=>{
console.log(error)
return 'error';
})
})
});
Thanks a lot in advance!

Answer 1

You should use Promise.all() instead of running each promise (fetch request) separately in a forEach loop. Also I don't see the function returning anything if result_array.length is not 2. I can see there are only 2 requests that you are making but it's good to handle all possible cases so try adding a return statement if the condition is not satisfied. Try refactoring your code to this (I've used an async function):
exports.restaurantSearch = functions.https.onCall(async (data, context) => {
// Do note the async ^^^^^
const request = data.request;
const k = encodeURIComponent(request);
const url1 = "an_url_to_call_the_external_API" + k;
const url2 = "another_url_to_call_the_external_API" + k;
const url_array = [url1, url2];
const responses = await Promise.all(url_array.map((url) => fetch(url, { headers: { "Authorization": "API_KEY" } })))
const responses_array = await Promise.all(responses.map((response) => response.json()))
console.log(responses_array)
const result_array: any[] = responses_array.map((res) => res.documents)
// Although this if statement is redundant if you will be running exactly 2 promises
if (result_array.length === 2) {
const new_result_array_2 = [...new Set((result_array))];
const info_array = new_result_array_2.map(({place_name, address_name}) => ({place_name, address_name}))
return {data: info_array}
}
return {error: "Array length incorrect"}
});
If you'll be running 2 promises only, other option would be:
// Directly adding promises in Promise.all() instead of using map
const [res1, res2] = await Promise.all([fetch("url1"), fetch("url2")])
const [data1, data2] = await Promise.all([res1.json(), res2.json()])
Also check Fetch multiple links inside of forEach loop