Loading a level

Cocos Creator
#1

How can I make the game check when a new scene is initialized? I would like to make a loading screen with a progress bar

#2 
    loadScene(sceneName: string) {
        this.progressBar.progress = 0;
        this.progressBar.node.active = true;
        director.preloadScene(sceneName, (loaded, total) => {
            this.progressBar.progress = loaded / total;
            console.log("onLoading: " + loaded + "/" + total);
        }, (err, scene) => {
            if(err) return
            director.loadScene(sceneName);
        })
    }