This is the first working draft of a visitor sign-in log for my workplace.

The final copy includes more error-checking for signing out, extra code to deal with the possibility that the app is left running over midnight and a fair bit of prettying up.

visitors.js

//Visitor sign-in app by Steve Garman
//saves one day's data as a JSON string in a file
 
//Global variables
var recArray = [], fileFolder = "/sdcard/sjgApps/", jsonPath;
//Global layouts and controls
var scrollr, layScroll, edtName, edtOrg, edtVehicle,edtReason;
 
//Called when application is started.
function OnStart(){
  //file variables
  var d = new Date();
  jsonPath = fileFolder + "vistorBook" +
     d.toISOString().slice(0,10).replace(/-/gi,"_")
     + ".json";
  app.MakeFolder(fileFolder)
  //Create main layout.
  var lay = app.CreateLayout( "linear", "Left" );
  //Create a scroller and add it to main layout
  scrollr = app.CreateScroller( 1.0, 0.8 ); 
  lay.AddChild( scrollr );  
  //Create a layout inside scroller. 
  layScroll = app.CreateLayout( "Linear", "Left");
  scrollr.AddChild( layScroll );
 
  //Create a sign-in layout
  var layNew = app.CreateLayout( "linear", "Horizontal,Left");
  edtName = app.CreateTextEdit("", .16);
  edtName.SetHint("Name");
  layNew.AddChild(edtName);
  edtOrg = app.CreateTextEdit("", .16);
  edtOrg.SetHint("Organization");
  layNew.AddChild(edtOrg);
  edtVehicle = app.CreateTextEdit("", .16);
  edtVehicle.SetHint("Vehicle reg.");
  layNew.AddChild(edtVehicle);
  edtReason = app.CreateTextEdit("", .16);
  edtReason.SetHint("Reason for visit");
  layNew.AddChild(edtReason);
  var btnCreate = app.CreateButton("Ok");
  btnCreate.SetOnTouch(btnCreate_OnClick);
  layNew.AddChild(btnCreate);
 
  //Add sign-in layout to main layout
  lay.AddChild(layNew);
 
  //Add main layout to app.    
  app.AddLayout( lay );
  //check if today's visitor book already active.
  if(app.FileExists(jsonPath)){
    loadJSONfile();
  }
}//OnStart
 
function btnCreate_OnClick( ){
  app.HideKeyboard();
  var name = edtName.GetText();
  var org = edtOrg.GetText();
  var reg = edtVehicle.GetText();
  var reason = edtReason.GetText();
  //check required fields
  var errs = "";
  if ( name == "" ) errs = "'Name' ";
  if ( reason == "" ) errs = errs + "'Reason for visit' ";
  if ( errs != ""){
    //bail out
    app.Alert( errs + "cannot be empty");
    return;
  }
  // clear sign-in form for next visitor
  edtName.SetText("");
  edtOrg.SetText("");
  edtVehicle.SetText("");
  edtReason.SetText("");
  // create a record
  var obj = {};
  obj.name = name;
  obj.org = org;
  obj.reg = reg;
  obj.reason = reason;
  var d = new Date();
  obj.timeIn = d.toTimeString().slice(0,5);
  obj.timeOut = "Out";
  // add this record to the array
  recArray.push( obj );
  saveJSONfile();
  // display record on scroller
  layScroll.AddChild( recordLayout(obj) );
  scrollr.ScrollTo(0, layScroll.GetHeight());
}//btnCreate_OnClick
 
function btnOut_OnClick( ){
  //has this visitor already signed out?
  if (this.GetText() != "Out") return;
  //not yet, so record time out
  var d = new Date();
  this.obj.timeOut = d.toTimeString().slice(0,5);
  this.SetText(this.obj.timeOut);
  //update copy of recArray on file
  saveJSONfile();
}//btnOut_OnClick
 
function recordLayout(obj){
  //create a new horizontal layout to display this record
  var newlay = app.CreateLayout( "Linear", "Horizontal,FillXY" );
  var txt = app.CreateText(obj.name, 0.15);
  newlay.AddChild(txt);
  txt = app.CreateText(obj.org, 0.15);
  newlay.AddChild(txt);
  txt = app.CreateText(obj.reg, 0.15);
  newlay.AddChild(txt);
  txt = app.CreateText(obj.reason, 0.15);
  newlay.AddChild(txt);
  txt = app.CreateText(obj.timeIn, 0.15);
  newlay.AddChild(txt);
  var btn = app.CreateButton(obj.timeOut, 0.15);
  btn.obj = obj;
  btn.SetOnTouch(btnOut_OnClick);
  newlay.AddChild(btn);
  return newlay;
}//recordLayout
 
function saveJSONfile(){
  //update copy of recArray on file
  var s = JSON.stringify(recArray);
  app.WriteFile(jsonPath, s )
}//saveJSONfile
 
function loadJSONfile(){
  //read copy of recArray from file
  var s = app.ReadFile(jsonPath)
  recArray = JSON.parse(s)
  var len = recArray.length;
  for (var i=0; i<len;i++){
    var obj = recArray[i];
    layScroll.AddChild( recordLayout(obj) );
  }
  scrollr.ScrollTo(0, layScroll.GetHeight());
}//loadJSONfile