CODEWITHSUNDEEP
javascriptnode.jsmongodbreact-native
Omar Diaa
Omar Diaa

Reputation: 286

How to put a fetch request inside a function and wait for the return value when I call the function

I am using react-native, mongo DB and node js and I need to create some database functions and put them in some modules to be able to reuse them whenever I want. To fetch data from the mongo database, I use the fetch() function which returns a promise. So, for all functions that I created that did not return a value, I used .then and I faced no problems. On the other side, when I return a value inside a fetch().then() function and use this returned value, I get undefined. The code I use for the function looks like:

export const getUsers = () => {
  //I cannot use this function because of returning a promise
  fetch("http://1jjsd12zaws.ngrok.io/database/", {
    method: "GET",
    headers: {
      "Content-Type": "application/json",
    },
  })
    .then((res) => {
      res.json();
    })
    .then((data) => {
      return JSON.stringify(data);
    });
};

Then, when I try to run this code:

let users=getUsers();
console.log(users);

It prints undefined.

What I think is going on is that the console.log(users) runs before getUsers() returns its value. But I do not know why does this happen and I want it to wait for getUsers() to execute then, completes its work.

Upvotes: 0

Views: 2581

Answers (2)

Hamza El Aoutar
Hamza El Aoutar

Reputation: 5657

  • You need to return fetch(..) inside getUsers (that's why you are getting undefined)
  • You also need to return res.json() inside the first then
  • Since getUsers returns a Promise, then you need to use .then (or async/await) to access the promise value: getUsers().then(users => {...})

const getUsers = () => {
  return fetch('http://1jjsd12zaws.ngrok.io/database/', {
    method: 'GET',
    headers: {
      'Content-Type': 'application/json'
    }
  })
    .then(res => {
      return res.json();
    })
    .then(data => {
      return JSON.stringify(data);
    });
};

getUsers().then(users => console.log(users))

Upvotes: 3

BenMiriello
BenMiriello

Reputation: 1

Async and await should cover it. The example on MDN docs explains it better than I can and should apply to your use case.

Upvotes: 0

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