Editor GUI error

Im making a hangman game, and i need to use the EditorGUI.BeginChangeCheck function, however it requires me to put the script in an editor folder, as i have done. Now, it gives me this error "The class defined in the script is not derived from MonoBehaviour or ScriptableObject!" any help will be appreciated!

 public var word : String;
 
 static var typeArea : String[];
 
 private var lastWord : String;
 
 static var lastLetterSet : String[];
 
 public var typeAreaStyle : GUIStyle;
 
 
 // *****************BODY CODE AREA********************************
 
 function Update() {
 
     if(lastWord != word)
     {
         DivideTextArea();
     }
     
     //CheckIfCorrect();
 
 }
 
 function DivideTextArea() {
 
     lastWord = word;
     
     typeArea = new String[word.Length];
     
     for(i = 0; i < typeArea.Length; i++)
     {
         typeArea[i] = "_";
     }
 
 }
 
 function OnGUI() {
     EditorGUI.BeginChangeCheck ();    
     
     var textPosX = 25;
     
     var textPosY = Screen.height - 50;
     
     lastLetterSet = new String[typeArea.Length];
     
     for(i = 0; i < typeArea.Length; i++)
     {
         typeArea[i] = GUI.TextField(Rect(textPosX, textPosY, 50, 50), typeArea[i], 1, typeAreaStyle);
         
         if(GUI.changed)
         {
             GUI.changed = true;
         }
         
         textPosX += 75;
         
         if(typeArea[i] == "")        //reset to underscore if area is empty
         {
             typeArea[i] = "_";
         }
     
     }
     
     if(EditorGUI.EndChangeCheck())
     {
         CheckIfCorrect();
         GUI.changed = false;
     }
 
 }
 
 function CheckIfCorrect() {
 
     for(i = 0; i < typeArea.Length; i++)
     {
         if(typeArea[i] != "_")
         {
             if(typeArea[i] == word[i])
             {
                 Debug.Log("you are correct");
             }
         }    
     }
 
 }