TypeError: _super.call is not a function(…)

GUILayout.ts

import GUIElement = require('./GUIElement');

class GUILayout extends GUIElement implements IGUILayout {
    // Public members
    public panels: Array<GUIPanel> = new Array<GUIPanel>();

    /**
     * Constructor
     * @param name layout name
     * @param app App instance
     */
    constructor(name: string, app: App) {
        super(name, app);
    }
}