Web page with some JavaScript to help with using https://wa.me for sending a WhatsApp message to a telephone number
With this, you can use https://wa.me/ to send a WhatsApp message to a telephone number by means of a web browser, meant mainly to be used on a desktop pc, but it should also work on a smartphone (I tested it and got it working in Chrome and Firefox on Android). It assumes you are either using the WhatsApp (desktop) client or WhatsApp Web in the same browser.
To use this, you need a web server. Which software you use for the web server, is irrelevant, as it is just a static HTML page with some JavaScript and CSS. For your convenience, I've set up a Docker container with Nginx. You can find the Docker repository at https://hub.docker.com/repository/docker/richy6378/whatsapp-helper.
Uses Flag Icons by FamFamFam.