Unable to locate emscripten
Solution 1:
Ubuntu 20.04 LTS misses this package in official repositories.
You can download this package from previous 18.04 LTS release and install it manually by using commands below:
cd ~/Downloads
wget -c http://archive.ubuntu.com/ubuntu/pool/universe/e/emscripten/emscripten_1.22.1-1build1_amd64.deb
sudo apt-get install ./emscripten_1.22.1-1build1_amd64.deb