How to prevent browser default page saving dialog pop-out in GrapesJS saving command

Question

I would like know to how to prevent browser default page saving dialog pop-out when clicking CTRL+ S. Below is my command code for saving function of GrapesJS

keymaps.add('ns:save-keymap', '⌘+s, ctrl+s',  editor => {
    editor.runCommand('save-db');
});

editor.on('keymap:emit', (id, shortcut, event) => {
    switch(id){
        case 'ns:save-keymap':
            event.preventDefault();
            event.stopPropagation();
            //alert('Saving template...');
            break;
    }
});

Bypass browser default page saving dialog pop-out in GrapesJS saving command. Although event.preventDefault(); already put into event trigger, but seem not working.

Thanks