JSFiddle - React, Tailwind, and code Playground

HTML

<div id="container">
            <p>some sample test<a href="test.html" title="a test title">Test</a>test test scenarios test2 notest3.</p>
        <script>
            var test = true;
        </script>
</div>

JavaScript

// Reusable generic function
function surroundInElement(el, regex, surrounderCreateFunc) {
    // script and style elements are left alone
    if (!/^(script|style)$/.test(el.tagName)) {
        var child = el.lastChild;
        while (child) {
            if (child.nodeType == 1) {
                surroundInElement(child, regex, surrounderCreateFunc);
            } else if (child.nodeType == 3) {
                surroundMatchingText(child, regex, surrounderCreateFunc);
            }
            child = child.previousSibling;
        }
    }
}

// Reusable generic function
function surroundMatchingText(textNode, regex, surrounderCreateFunc) {
    var parent = textNode.parentNode;
    var result, surroundingNode, matchedTextNode, matchLength, matchedText;
    while ( textNode && (result = regex.exec(textNode.data)) ) {
        matchedTextNode = textNode.splitText(result.index);
        matchedText = result[0];
        matchLength = matchedText.length;
        textNode = (matchedTextNode.length > matchLength) ?
            matchedTextNode.splitText(matchLength) : null;
        // Ensure searching starts at the beginning of the text node
        regex.lastIndex = 0;
        surroundingNode = surrounderCreateFunc(matchedTextNode.cloneNode(true));
        parent.insertBefore(surroundingNode, matchedTextNode);
        parent.removeChild(matchedTextNode);
    }
}

// This function does the surrounding for every matched piece of text
// and can be customized  to do what you like
function createSpan(matchedTextNode) {
    var el = document.createElement("span");
    el.style.color = "red";
    el.appendChild(matchedTextNode);
    return el;
}

// The main function
function wrapWords(container, words) {
    // Replace the words one at a time to ensure "test2" gets matched
    for (var i = 0, len = words.length; i < len; ++i) {
        surroundInElement(container, new RegExp(words[i]), createSpan);
    }
}

wrapWords(document.getElementById("container"), ["test2", "test"]);