JSFiddle - React, Tailwind, and code Playground

HTML

<textarea id='eC'>
</textarea><br/>
<input type='radio' name='mode' value='alert' />Alert<br/>
<input type='radio' name='mode' value='console' checked='checked'/>Console.log<br/>
<input type='button' id='test' value='Test code!' />

JavaScript

document.querySelector('#test').addEventListener('click', (function(radios, txt)
{
    return function()
    {
        var mode,
            string = txt.value.replace(/(?!>)\b(hello)\b(?!<)/gi, '<b>$1</b>');
        if (radios.item(0).checked)
            mode = radios.item(0).value;
        else
            mode = radios.item(1).value;
        if (mode === 'alert')
            alert(string);
        else
            console.log(string);
        if (confirm('Replace text?'))
            txt.value = string;
    };
}(document.querySelectorAll('input[name=mode]'),document.querySelector('#eC'))),false);