Phonegap: Update query for Local Database

I am trying to develop an app in phonegap that use Local Database.I create the database and table. But when I try to updating the content its not updating.Am getting the alert us "updating".

 db = window.openDatabase("DirectoryDB", "1.0", "DB", 200000);
if (dbCreated){
    db.transaction(updateShapes, transaction_error);
}
else{
    db.transaction(populateDB, transaction_error, populateDB_success);
}

function populateDB(tx) {
 var sqlShape = "CREATE TABLE IF NOT EXISTS shapeList ( "+"id INTEGER PRIMARY KEY AUTOINCREMENT, "+"shape_id INTEGER  ," +"status VARCHAR(200),"+"purchase_stataus VARCHAR(200))";
  tx.executeSql(sqlShape);

  tx.executeSql("INSERT INTO shapeList (shape_id,status,purchase_stataus) VALUES (4,'paid','n')");
}
}

 function populateDB_success() 
{
  dbCreated = true;
  db.transaction(getImages, transaction_error);
}
function updateShapes(tx)
{
  alert("updating");
  var strResult = "4";
  var status = "y";
  tx.executeSql("UPDATE shapeList SET purchase_stataus='status' WHERE shape_id='+ strResult+'");
}

Can any please tell me the mistake of the code . Thanks in advance