Open Source Components
Bootstrap 4 Extensions
bootstrap-input-spinner
A Bootstrap 4 / jQuery plugin to extend input elements for numbers in such a way that they offer a particularly simple input option via +/- buttons. Numbers are displayed with correct localization.

bootstrap-show-notification
A Bootstrap 4 / jQuery plugin, for displaying notifications with JavaScript.

Other HTML Tools
auto-resize-textarea
Adjusts a <textarea> automatically to the height of the content. Also works with Bootstrap 4.
external-links-blank
All links contained in a website, who lead to an external page will automatically open in a new tab or window (target="_blank").