How can i check every directory in my device in ionic 3

Is there any way we can check directory and files from root directory with loop process in all its sub directories. I found a code but it needs first directory but i need it to be from root directory.

this._storage = cordova.file.externalDataDirectory;
this.file.checkDir(this.storage, ‘mydir’).then( => console.log(‘yay’)).catch(err => console.log(‘boooh’));

No. You can only see files and directories that belong to your app or are public. Files and directories belonging to other apps are not readable by your app.

Okay i cannot access to the directories that belongs to other apps but i can access to public files and folders. So how can i loop through public folders dynamically without knowing folder names like downloads, photos, music etc.