I've just installed a WordPress plugin known as "Simple MathJax". This is intended to allow the use of typeset mathematical notation in a WordPress blog, using a popular Javascript library for rendering mathematical equations.
The quadratic equation \(ax^2+bx+c=0\) has solution given by \[x = \frac{-b\pm\sqrt{b^2-4ac}}{2a}.\]
It indeed works.
Another thing I tried (not shown here): including a JavaScript/HTML5/Canvas app. The app I meant to include on my page was a simple demonstration of a cycloid (a curve produced by a point on the edge of a rolling circle). My app is at http://wclang.net/cycloid_2017-12-21.html. It turns out you can include such a page using an iframe tag (search for this to find instructions, but it's not difficult). But it does work (the interactivity or animation produced by your script will be functional). However, it's not very elegant; you see your page or app set in its own frame, with scrollbars as needed; perhaps it's better just to have a link to the other page, and not try to wrestle with WordPress on including scripts and Canvas elements.