Async JS/Node - Sequential Callbacks Example

example.js

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)
      })
    })
  })
}

var username = 'seanghagstrom'

findLikesForPostsByUsername(username, function(err, totalLikes) {
  if(err) {
    console.error(err)
  } else {
    console.log(username + ' total number of likes: ' + totalLikes)
  }
})