Async JS/Node - Sequential Callbacks Example - Part 1

example.js

// Part 1

function findLikesForPostsByUsername(username, callback) {
  findUserByUsername(username, function(err, user) {
    if(err) return callback(err)
    
    findPostsByUser(user, function(err, posts) {
      if(err) return callback(err)
      
      findLikesByPosts(posts, function(err, likes) {
        if(err) return callback(err)
        
        var totalLikes = likes.reduce(function(x, y) { return x + y })
        callback(null, totalLikes)
      })
    })
  })
}