an example for callback to promise conversion in javascript

callback_to_promise.js

console.log('Before');

// callback approach
// getUser(1, displayUser);


// promised based approach
// getUser(1)
//   .then(user => getRepositories(user.name))
//   .then(repos => getCommits(repos[0]))
//   .then(commits => console.log(commits))
//   .catch(err => console.log(err));


// async-await approach
async function displayUserCommits(){
  try {
    const user = await getUser(1);
    const repos = await getRepositories(user.name);
    const commits = await getCommits(repos[0]);  
    console.log(commits);    
  }
  catch(err){
    console.log(err);
  }
  
}

displayUserCommits();


console.log("After");


function getUser(id){
  return new Promise((resolve, reject) => {
    setTimeout(() => {
      console.log("Reading a user from database!");
      resolve({ id: id, name: "salmanx" });
    }, 2000)
  })
  
}

function getRepositories(username){
  return new Promise((resolve, reject) => {
    setTimeout(() => {
      console.log("Calling github api for repo");
      resolve(["repo1", "repo2", "repo3"]);
    }, 2000)
  })

}

function getCommits(repo){
  return new Promise((resolve, reject) => {
    setTimeout(() => {
      console.log("Calling github api for commits");
      resolve(["commit1", "commit2"]);
    }, 2000)
  })

}

function displayCommits(commits){
  console.log(commits);
}

function displayRepos(repos){
  getCommits(repos[0], displayCommits);
}

function displayUser(user){
  getRepositories(user.name, displayRepos)
}