You use Adobe's Flash IDE (now called "Adobe Animate") to compile ActionScript to a .swf binary file, which you then embed in a web page with an <object> or <embed> tag.

Adobe Animate can now export animations and scripts to HTML5: https://en.wikipedia.org/wiki/Adobe_Animate

Thanks. Does one always have to pay (Adobe Animate is trialware) to do Actionscript programming? Probably thats where I got stuck last time (wasnt looking too hard into paid solutions)

Flex [0] is the open source CLI compiler.

[0] https://en.wikipedia.org/wiki/Apache_Flex