This repl parses common LaTeX integral syntax and outputs a string that is easier to postfix.
To view this on TripleLog, click here.
The HTML is a simple input/output to change a string of text.
Add CSS by editing the style.css file that is linked to in the head section or inline edit the style section in the head.
The script.js file parses some LaTeX like integrals. It should handle \mathrm{d}x and dx as well as bounds in either a^b or {a+1}^{b+1} form.