JSFiddle - React, Tailwind, and code Playground

HTML

<div id="test">Testing
    <p>Some more text inside p</p>
    <p>asdasdasdasdasde p</p>
    Test
</div>

CSS

strong
{
    font-weight: bold;   
}

JavaScript

getTextNodes(document.getElementById("test"));

function getTextNodes(parent)
{
    var textNodes = [];
    var nodes = parent.childNodes;
    for(var i=0;i<nodes.length;i++)
    {
        if(nodes[i].nodeType === 3)
        {   
            textNodes.push(nodes[i]);
            wrapBold(nodes[i], parent);
        }
    }
}

function wrapBold(node, parent)
{
    if(node.data.match(/[^\t\n\r ]/))
    {
        var bold = document.createElement("strong");
        parent.insertBefore(bold, node);
        bold.appendChild(node);
    }else
    {
        return false;   
    }
}