Essentially the website is static site generated, same as jekyll or something. There is three parts to this process. HTML is written in input.html, the HTML in that file is embeded with javascript. Essentially this file is parsed and generates an output.js file that generates the index.html.
The syntax of input.html is as such:
This will need an import file that will supply it the data (foo and bar), in this branch its called import.js and knowing what variables to import, compiling this will output a js file that looks something like:
one thing to note here is compare the syntax for %%+foo%% vs %% for (let ... %% lines. The + in the %%+foo%% line marks that expression as variable to be added to html variable whereas not adding the + puts the expression as it is into the javascript file. If we added 'for (let i = 0 ...' to html like, 'html += for (let i = 0 ...', it would produce an error, hence the distinction is important.
Which will generate:
This is essentially it. If you know javascript, you already know this