Firebase cloud function: http function returns null

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!

Dharmaraj · Accepted Answer · 2021-08-22 11:01:41Z

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

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