Exploring the depths of async/await to redefine our commitments and gain a clearer understanding

Question

Exploring the depths of async/await to redefine our commitments and gain a clearer understanding

I have two functions that manage Facebook login/logout on my front-end using promises. I am interested in refactoring them with async/await.

The original code utilizing promises is as follows:

export function login() {
  return new Promise<facebookSdk.IAuthResponse>((resolve, reject) => {
    FB.login((response) => {
      if (response.authResponse) {
        resolve(response)
      } else {
        reject(errors.facebookLoginError)
      }
    })
  })
}

export function logout() {
  return new Promise<facebookSdk.IAuthResponse>((resolve) => {
    FB.logout((response) => {
      resolve(response)
    })
  })
}

Below is the modified version of these functions using async/await:

function promiseFacebookLogin(): Promise<facebookSdk.IAuthResponse | Error> {
  return new Promise<facebookSdk.IAuthResponse>((resolve, reject) => {
    FB.login((response) => {
      if (response.authResponse) {
        resolve(response)
      } else {
        reject(errors.facebookLoginError)
      }
    })
  })
}

export async function login(): Promise<facebookSdk.IAuthResponse | Error> {
  try {
    return await promiseFacebookLogin()
  } catch (err) {
    throw err
  }
}

export async function logout(): Promise<facebookSdk.IAuthResponse | void> {
  try {
    return await FB.logout((response) => {
      return response
    })
  } catch (err) {
    throw err
  }
}

The updated code now operates as intended, but there is a lingering question regarding the login function. While I was able to eliminate the use of Promises entirely in the logout function, for the login function, I had to keep the Promise syntax and wrap it separately before awaiting the result. Upon researching, it seems this approach is typical for dealing with callback-based functions.

Is there anyone who can offer insights into why it isn't feasible to completely remove the Promise syntax from the login function?

javascript typescript async-await es6-promise facebook-sdk-4.x

Answer 1

Answer №1

One of the reasons why you don't have to encapsulate the FB.logout function in a Promise wrapper is because you are simply executing it without utilizing the resolved value, essentially treating it as a "fire and forget" operation. You could achieve the same outcome by implementing the method like this:

export function logout(): void {
  try {
    FB.logout((response) => {
      // no action needed
    })
  } catch (err) {
    throw err
  }
}

On the other hand, if you require the value returned by FB.login, then wrapping it in a Promise is necessary in order to make use of it within an async/await scenario.

Answer 2

One of the reasons why you don't have to encapsulate the FB.logout function in a Promise wrapper is because you are simply executing it without utilizing the resolved value, essentially treating it as a "fire and forget" operation. You could achieve the same outcome by implementing the method like this:

export function logout(): void {
  try {
    FB.logout((response) => {
      // no action needed
    })
  } catch (err) {
    throw err
  }
}

On the other hand, if you require the value returned by FB.login, then wrapping it in a Promise is necessary in order to make use of it within an async/await scenario.

Answer 3

Answer №2

When we want to execute functions that return Promise instances, we use the keyword async. These functions can then be awaited within the body of other functions marked as async.

A common practice is to convert callback style APIs into Promise-based ones:

function fbLogin(..., cb) { ... }

async function genFbLogin(...args): Promise<*> {
  return new Promise((resolve, reject) => {
    fbLogin(...args, (error, result) => {
      if (error) {
        reject(error);        
      } else {
        resolve(result);
      }
    });
  });
}

In the provided example, the `login` function is already structured in this format. It returns a Promise, allowing for the placement of the `async` keyword before its declaration. The same applies to the `logout` function, which is also Promise-based rather than callback-based. To properly utilize the `logout` function, you should implement it as follows:

async function myLogoutHandler() {
  try {
    const response = await logout();
    console.log(response); // handle the result accordingly      
  } catch (e) {
    console.log('error', e);
  }
}

Make sure to include a `try-catch` block within your async functions to effectively manage any potential errors that may arise while awaiting promises.

Answer 4

When we want to execute functions that return Promise instances, we use the keyword async. These functions can then be awaited within the body of other functions marked as async.

A common practice is to convert callback style APIs into Promise-based ones:

function fbLogin(..., cb) { ... }

async function genFbLogin(...args): Promise<*> {
  return new Promise((resolve, reject) => {
    fbLogin(...args, (error, result) => {
      if (error) {
        reject(error);        
      } else {
        resolve(result);
      }
    });
  });
}

In the provided example, the `login` function is already structured in this format. It returns a Promise, allowing for the placement of the `async` keyword before its declaration. The same applies to the `logout` function, which is also Promise-based rather than callback-based. To properly utilize the `logout` function, you should implement it as follows:

async function myLogoutHandler() {
  try {
    const response = await logout();
    console.log(response); // handle the result accordingly      
  } catch (e) {
    console.log('error', e);
  }
}

Make sure to include a `try-catch` block within your async functions to effectively manage any potential errors that may arise while awaiting promises.

Answer 5

Answer №3

It is not possible to modify the export functions due to the restrictions imposed by the use of FB.login and FB.logout functions. These functions do not return a promise, which hinders any rewriting efforts. However, if Facebook were to update these functions to return a promise that resolves to the response (or throws an error if response.authResponse is false), then you could implement the solution recommended by @Saravana in his example.

For now, attempting to rewrite your current login and logout functions would only add unnecessary complexity. It is best to leave them as they are and simply await their execution when calling them elsewhere in your code. For example:

// Somewhere in your code base
async function someFunc() {
  try:
    // Wait for the response resolved in the callback function
    // within the FB.login call
    let fbLoginResponse = await login();

    // ... handle the response here ...

  catch (err) {
    // The error will be errors.facebookLoginError as it was rejected
    // in the callback function of the FB.login call
    console.log('Authentication failed! Please try again.');
  }
}

Answer 6

It is not possible to modify the export functions due to the restrictions imposed by the use of FB.login and FB.logout functions. These functions do not return a promise, which hinders any rewriting efforts. However, if Facebook were to update these functions to return a promise that resolves to the response (or throws an error if response.authResponse is false), then you could implement the solution recommended by @Saravana in his example.

For now, attempting to rewrite your current login and logout functions would only add unnecessary complexity. It is best to leave them as they are and simply await their execution when calling them elsewhere in your code. For example:

// Somewhere in your code base
async function someFunc() {
  try:
    // Wait for the response resolved in the callback function
    // within the FB.login call
    let fbLoginResponse = await login();

    // ... handle the response here ...

  catch (err) {
    // The error will be errors.facebookLoginError as it was rejected
    // in the callback function of the FB.login call
    console.log('Authentication failed! Please try again.');
  }
}

Exploring the depths of async/await to redefine our commitments and gain a clearer understanding

Answer №1

Answer №2

Answer №3

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