var db = openDatabase("example_db", "", "Example Database", 100000);
// openDatabase(db name, required version (blank string for n/a), human-readable database name, expected size in bytes)

db.changeVersion("", "1", function(t){
  t.executeSql("create table ...");
});

/* Note:
openDatabase actually takes one more (optional) argument -- a callback in case the database was /just/ created, for you to call changeVersion and provide an initial schema.  However, since this post is more interested in migrations, and because I don't want the initial migration to be a "special case", I'm pretending like it doesn't exist.  It's there if you want it, of course.
*/