JSFiddle - React, Tailwind, and code Playground

HTML

<div class="prewrap">
<div class="pretitle">
    Vector field describing ($dr/d\theta$, r) for the parabola $y = x^2$ (matlab code)
    <div class="codeclick">Click to show code</div>
</div>
<pre>
x = -2:.01:2
y = x.^2
plot(x, y)
hold on
xvec = -1.8:0.2:1.8
yvec = xvec.^2
scatter(xvec, yvec)
vvec = sqrt(xvec.^2 + yvec.^2)
uvec = vvec ./ xvec
quiver(xvec, yvec, uvec, vvec)
</pre>
</div>

JavaScript

function hidepre() {
    var pre = this.getElementsByTagName("pre")[0]
    if (pre.style.display === "none") {
        pre.style.display = "block";
    } else {
        pre.style.display = "none";
    }
}
function hidepreall() {
    var prewraps = document.getElementsByClassName("prewrap");
    if(prewraps.length > 0) {
        for (var i = 0; i < prewraps.length; i++) {
            var prewrap = prewraps[i];
            prewrap.onclick = hidepre;
        }
    }
}