Framework7 vue preloader error

Im trying to call a preloader using framework7 vue while doing this:
const self = this;
f7.dialog.preloader("Please wait...");

but I get this error when doing so:
Uncaught TypeError: $containerEl is undefined Modal webpack://horizontalscroll/./node_modules/framework7/esm/components/modal/modal-class.js?:42 Dialog webpack://horizontalscroll/./src/js/app.js_+_119_modules?:139 preloader webpack://horizontalscroll/./src/js/app.js_+_119_modules?:576

How could I fix this issue? Seems that something is wrong from within f7 files, but not sure.

Could I get any help?
Still stuck with this issue.