JSFiddle - React, Tailwind, and code Playground

HTML

Test * test

<div>Test * test</div>
<div>
    <div>Test * test</div>
    <div>Test * test * test</div>
</div>
<p>
    Test * test
</p>

CSS

div {
    border: 1px solid;
    margin: 10px;
}

.red {
    color: #f00;
}

JavaScript

var specialTags = ["script", "style"].join("|"),
    re = new RegExp("^(?:" + specialTags + ")$", "i");

for (var els = document.getElementsByTagName("*"), i = els.length; i--;) {
    var el = els[i],
        tag = el.tagName;

    if (re.test(tag))
        continue;

    for (var j = 0, childs = el.childNodes, lj = childs.length; j < lj; j++) {
        var child = childs[j];
        if (child.nodeType === 3 && child.nodeValue.indexOf("*") > -1) {
            var segments = child.nodeValue.split("*");
            for (var k = 0, lk = segments.length; k < lk; k++) {
                el.insertBefore(document.createTextNode(segments[k]), child);
                if (k < lk - 1) {
                    var span = document.createElement("span");
                    span.className = "red";
                    span.appendChild(document.createTextNode("*"));
                    el.insertBefore(span, child);
                }
            }
            el.removeChild(child);
        }
    }
}