[Supplemental, NoInterfaceObject]
interface WindowDatabase {
Database openDatabase(in DOMString name, in DOMString version, in DOMString displayName, in unsigned long estimatedSize, in optional DatabaseCallback creationCallback);
};
Window implements WindowDatabase;

[Supplemental, NoInterfaceObject]
interface WorkerUtilsDatabase {
Database openDatabase(in DOMString name, in DOMString version, in DOMString displayName, in unsigned long estimatedSize, in optional DatabaseCallback creationCallback);
DatabaseSync openDatabaseSync(in DOMString name, in DOMString version, in DOMString displayName, in unsigned long estimatedSize, in optional DatabaseCallback creationCallback);
};
WorkerUtils implements WorkerUtilsDatabase;

[Callback=FunctionOnly, NoInterfaceObject]
interface DatabaseCallback {
void handleEvent(in Database database);
};

2,SQLTransaction接口,关注executeSql方法

typedef sequence<any> ObjectArray;

interface SQLTransaction {
void executeSql(in DOMString sqlStatement, in optional ObjectArray arguments, in optional SQLStatementCallback callback, in optional SQLStatementErrorCallback errorCallback);
};

[Callback=FunctionOnly, NoInterfaceObject]
interface SQLStatementCallback {
void handleEvent(in SQLTransaction transaction, in SQLResultSet resultSet);
};

[Callback=FunctionOnly, NoInterfaceObject]
interface SQLStatementErrorCallback {
boolean handleEvent(in SQLTransaction transaction, in SQLError error);
};

3,最后看下SQLResultSetRowList定义

interface SQLResultSetRowList {
readonly attribute unsigned long length;
getter any item(in unsigned long index);
};

和SQLResultSet定义

1 interface SQLResultSet {
2 readonly attribute long insertId;
3 readonly attribute long rowsAffected;
4 readonly attribute SQLResultSetRowList rows;
5 };

类图

由于window对象实现了WindowDatabase接口,从而可以直接在window对象上调用openDatabase等方法
同时实现WindowDatabse接口的还有WorkerUtils对象