callback vs promises

promises

function logWord(word){
   setTimeout(function() {
       console.log(word)
   }, Math.floor(Math.random() * 100) + 1
   // return value between 1 ~ 100
   )
}

function logAll(){
   logWord("A")
   logWord("B")
   logWord("C")
}
logAll()


// Callbacks

function logWord(word, callback) {
   setTimeout(function() {
       console.log(word)
       callback()
   }), Math.floor(Math.random() * 100) + 1
}

function logAll(){
   logWord("A", function() {
       logWord("B", function() {
           logWord("C", function() {})
       })
   })
}
// Callback Hell
logAll()

// Promises

function logWord(word) {
   return new Promise(function (resolve, reject) {
       setTimeout(function() {
           console.log(word)
           resolve()
       }, Math.floor(Math.random() * 100) + 1)
   })
}

function logAll() {
   logWord('A')
   .then(function() {
       return logWord('B')
   })
   .then(function() {
       return logWord('C')
   })
}

logAll()