Vector map rendering (https://www.mapbox.com/blog/mapbox-gl-js/) editors (https://atom.io/) data visualization (https://github.com/mbostock/d3/wiki/Gallery) compressing data (https://www.npmjs.com/package/gzip-js) image manipulation (https://www.npmjs.com/search?q=jpeg)

My point is: almost anything can be build with Javascript.