EditorPrefs.HasKey  

// Simple Editor Script that lets you create / save quick notes
// Between Unity Sessions.

class QuickNotes extends EditorWindow {

var note : String = "Notes:\n->\n->";

@MenuItem("Examples/QuickNotes")
static function Init() {
var window = GetWindow(QuickNotes);
window.Show();
}
function OnGUI() {
note = EditorGUILayout.TextArea(note,
GUILayout.Width(position.width-5),
GUILayout.Height(position.height - 30));
EditorGUILayout.BeginHorizontal();
if(GUILayout.Button("Reset"))
note = "";
if(GUILayout.Button("Clear Story",GUILayout.Width(72))) {
note = "Notes:\n->\n->";
}
EditorGUILayout.EndHorizontal();
}
function OnFocus() {
if(EditorPrefs.HasKey("QuickNotes"))
note = EditorPrefs.GetString("QuickNotes");
}
function OnLostFocus() {
EditorPrefs.SetString("QuickNotes",note);
}
function OnDestroy() {
EditorPrefs.SetString("QuickNotes",note);
}
}