As of version 8, the mmenu.js plugin only supports ECMAScript 6 compliant browsers.
For Internet Explorer 10 and 11, you''ll need some polyfills.
Version 7 should work to some degree in Internet Explorer 9, but you'll need a matchMedia polyfill, version 6 should work in Internet Explorer 9 without any shortcomings.
This project uses Gulp(4) to compile, minify and concatenate the TS/JS and SCSS/CSS files. If you are unfamiliar with Gulp, check this tutorial on how to get started.
gulp watch in the command-line to put a watch on the files and run all scripts immediately after saving your changes.