I have been learning AngularJS and have written my first app. It's a Hangman AI which learns words and guesses the solution based on the words it knows.Please look over my code and provide some pointers towards better practices, techniques and overall criticism.Here is a CodePen demo, as the Stack Snippet may have cross-site AJAX issues.var app = angular.module(HangManAI, []);app.controller('HangManController', ['$scope', '$http', function($scope, $http){ $scope.step = 0; $scope.theWords   = new Array(); $scope.wordCount   = 0; $scope.wordLetters   = new Array(); $scope.myGuess    = None; $scope.testString  = ; $scope.attempts   =10; $scope.letterFound  = false; $scope.myMouth   = G'Day. I am a hangman AI written with AngularJS. I can win a game of hangman against you if I know the words you use. Click New Game to begin.; $scope.error   = ;  var availableLetters  = [A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T, U, V, W, X, Y, Z]; var knownWords = [];  //Functions $scope.startAGame = function(){  $scope.theWords = new Array();  $scope.wordCount = 0;  $scope.attempts = 10;  $scope.error = ;  availableLetters  = [A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T, U, V, W, X, Y, Z];  $scope.myMouth = Alright! First tell me how many words there are and how many letters for each word.;  $scope.step = 1;  var req = {    method: 'GET',    url: 'http://www.hott-source.com/hangman/getMemory.php',    data: { }   }   $http(req).then(function(response){    knownWords = response.data;    $scope.testString = knownWords;       }, function(response){    $scope.error = I could not get my memory. Try reloading the page.;   }); } $scope.checkWords = function(){  //Loop through each typed word  var i = $scope.theWords.length;  var wordKnown = false;  var newWords = ;  var whatToSay = ;  while(i--){   var currentWord = $scope.theWords[i].word;   //Check if we know it.   if(typeof knownWords[currentWord.length-1] === 'undefined')   {       }   else{    var innerLoop = knownWords[currentWord.length-1].length;    while(innerLoop--){     if(knownWords[currentWord.length-1][innerLoop] == currentWord)     {      wordKnown = true;     }    }   }   if(!wordKnown)   {    if(newWords != )    {     newWords += :;     whatToSay += , ;    }    else     whatToSay = I didn't know these words; ;    newWords += currentWord;    whatToSay += currentWord;   }   $scope.step=5;   $scope.error = whatToSay;  }  //This needs to save to memory    var myUrl = 'http://www.hott-source.com/hangman/getMemory.php';  if(newWords != )   myUrl += '?newWords='+newWords;    var req = {   method: 'GET',   url: myUrl,   data: { }  }  $scope.myMouth = ;  $http(req).then(function(response){   $scope.myMouth = Do you want to play again?;  }, function(response){   $scope.myMouth = I could not get my memory. Try reloading the page.;  }); } $scope.nextLetter = function() {  if($scope.letterFound)   $scope.letterFound = false;  else   $scope.attempts -=1;    if($scope.attempts > 0)   chooseALetter();  else  {   $scope.myMouth = Damn it... please show me the missing letters. Each click will change the letter. Click done when its right;   $scope.step = 4;  } } $scope.fixLetter = function(letterIndex, wordIndex) {  var aWord = this.theWords[wordIndex].word;  var aLetter = aWord[letterIndex];  switch(aLetter)  {   case A:    aLetter = B;    break;   case B:    aLetter = C;    break;   case C:    aLetter = D;    break;   case D:    aLetter = E;    break;   case E:    aLetter = F;    break;   case F:    aLetter = G;    break;   case G:    aLetter = H;    break;   case H:    aLetter = I;    break;   case I:    aLetter = J;    break;   case J:    aLetter = K;    break;   case K:    aLetter = L;    break;   case L:    aLetter = M;    break;   case M:    aLetter = N;    break;   case N:    aLetter = O;    break;   case O:    aLetter = P;    break;   case P:    aLetter = Q;    break;   case Q:    aLetter = R;    break;   case R:    aLetter = S;    break;   case S:    aLetter = T;    break;   case T:    aLetter = U;    break;   case U:    aLetter = V;    break;   case V:    aLetter = W;    break;   case W:    aLetter = X;    break;   case X:    aLetter = Y;    break;   case Y:    aLetter = Z;    break;   case Z:    aLetter = A;    break;   default:    aLetter = A;  }  aWord = aWord.replaceAt(letterIndex, aLetter);  this.theWords[wordIndex].word = aWord; } $scope.foundLetter = function(letterIndex, wordIndex) {  $scope.letterFound = true;  var aWord = this.theWords[wordIndex].word;  aWord = aWord.replaceAt(letterIndex, this.myGuess);  this.theWords[wordIndex].word = aWord;  var hasNotFinished = false;  for(var i = 0; i<this.wordCount; i++)  {   var theWord = this.theWords[i].word;   var j = theWord.length;   while(j--){    if(theWord[j] == _)    {     hasNotFinished = true;     break;    }   }   if(hasNotFinished)    break;  }  //Make some way to reverse  if(!hasNotFinished)  {   $scope.myMouth = YAY!, I GOT IT;   $scope.checkWords();  } } $scope.createTempWords = function(){  //If the word array is bigger than the number of words we want, slice it.  if(this.theWords.length > this.wordCount)   this.theWords = this.theWords.slice(0, -1);  else  {   //Otherwise push in another word.   for(var i = this.theWords.length; i<this.wordCount; i++)   {    this.theWords.push({id:i, word: _, letters:1});   }  } } //Increase or decrease the size of the words $scope.wordSize = function(num){  if(this.theWords[num].word.length > this.theWords[num].letters)   this.theWords[num].word = this.theWords[num].word.substr(0, this.theWords[num].letters);  else  {   //Otherwise push in another word.   for(var i = this.theWords[num].word.length; i<this.theWords[num].letters; i++)   {    this.theWords[num].word += _;   }  } } //Player has finished inputting their words. $scope.readyToPlay = function(){  if($scope.theWords.length < 1)   $scope.myMouth = You need to enter some words first.;  else{   $scope.instructions = Click the button which matches the letter location, or click no!;   $scope.step = 2;   chooseALetter();  } } //Enables me to delete an element from an array based on value.  Array.prototype.deleteElem = function(val) {  var index = this.indexOf(val);   if (index >= 0) this.splice(index, 1);  return this; } //Enables me to replace a character at a set index of a string String.prototype.replaceAt=function(index, character) {  return this.substr(0, index) + character + this.substr(index+character.length); } //Choose the most likely letter out of all known words with the lengths equal to the words in the phrase. function chooseALetter() {  var letterCount = [];  for(var i=0;i<availableLetters.length;i++){   letterCount[i] = 0;  }  //Loop through each secret word  for(var phraseWord_i = 0; phraseWord_i<$scope.theWords.length; phraseWord_i++)  {   var thisPhraseWord = $scope.theWords[phraseWord_i].word;   var phraseWordLength = thisPhraseWord.length;   //Loop through all the words of the same length   if(typeof knownWords[phraseWordLength-1] === 'undefined')   {       }   else   {    for(var knownWord_i = 0; knownWord_i<knownWords[phraseWordLength-1].length; knownWord_i++){     var thisKnownWord = knownWords[phraseWordLength-1][knownWord_i];     //     var i = thisKnownWord.length;     var canUse = true;     //Check if this word is allowed to be used     while (i--) {      //Has this letter been discovered?       if(thisPhraseWord[i] != _){        //Does thisKnownWord match that letter        if(thisPhraseWord[i] != thisKnownWord[i]){         canUse = false        }       }     }     //If this word can use add 1 to all the letterCounts     if(canUse){      var i = thisKnownWord.length;      while(i--){       letterCount[availableLetters.indexOf(thisKnownWord[i])] += 1;      }     }    }   }  }       //Find the most used letter  var maxIndex = 0;  var max = letterCount[0];    for (var i = 1; i < letterCount.length; i++) {   if (letterCount[i] > max) {    maxIndex = i;    max = letterCount[i];   }  }    $scope.myGuess = availableLetters[maxIndex];  $scope.myMouth = Are there any  + $scope.myGuess + 's in your phrase?;  availableLetters.deleteElem(availableLetters[maxIndex]); }}]);app.filter('isPlural', function(){ return function(input) {  if(input > 1 || input == 0)   return s;  else   return ; }});app.filter('dashes', function(){ return function(input) {  var result = ;  for(var i =0; i<input.length; i++)  {   result += _ ;  }  return result; }});.error{  color: red;}.inLineList{  list-style: none;  float: left;  padding-right: 20px;}p{  clear:left;}<script src=https://ajax.googleapis.com/ajax/libs/angularjs/1.2.23/angular.min.js></script><body ng-app=HangManAI>   <script src=http://ajax.googleapis.com/ajax/libs/angularjs/1.4.8/angular.min.js></script>  <div ng-controller='HangManController'>  <p>{{myMouth}}</p>  <p class='error'>{{error}}</p>  <div ng-show='step == 0'>   <button ng-click='startAGame()'>New Game</button>  </div>  <div ng-show='step==1'>   <input type='number' ng-model='wordCount' ng-change='createTempWords()' min=0>   <p>You want {{wordCount}} word{{wordCount | isPlural}}</p>   <ol>    <li ng-repeat='aWord in theWords track by $index'><input type='number' ng-model='aWord.letters' ng-change='wordSize($index)' ng-show='!gameOn'><button ng-click='foundLetter($index, $parent.$index)' ng-disabled='!gameOn' ng-repeat='letter in aWord.word track by $index'>{{ letter }}</button> {{aWord.letters}} letter{{aWord.letters | isPlural}}</li>   </ol>   <button id='startGame' ng-click='readyToPlay()' ng-show='!gameOn'>Start The Game</button>  </div>  <div ng-show='step==2'>   <p>I have {{attempts}} time{{attempts | isPlural}} I can guess wrong</p>   <ol>    <li class='inLineList' ng-repeat='aWord in theWords track by $index'><button ng-click='foundLetter($index, $parent.$index)' ng-repeat='letter in aWord.word track by $index'>{{ letter }}</button></li>   </ol>   <p><button ng-show='!letterFound' ng-click='nextLetter()'>No</button><button ng-show='letterFound' ng-click='nextLetter()'>Next Letter</button></p>  </div>  <div ng-show='step==4 || step==5'>   <ol>    <li ng-repeat='aWord in theWords track by $index'><button ng-click='fixLetter($index, $parent.$index)' ng-repeat='letter in aWord.word track by $index'>{{ letter }}</button></li>   </ol>   <p><button ng-show='step==4' ng-click='checkWords()'>Done</button></p>   <p><button ng-show='step==5' ng-click='startAGame()'>New Game</button></p>  </div> </div>  <script src='js/modules/HangManAI.js'></script> <script src='js/controllers/HangManController.js'></script> <script src='js/filters/isPlural.js'></script> <!--<script src='js/services/getMemory.js'></script>--></body></html>
Hangman learning AI
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