JSFiddle - React, Tailwind, and code Playground

HTML

<span class="price">TEST test.</span>
<span class="price">test TEST.</span>
<span class="price">TeSt TeSt.</span>
<span class="price">tEsT tEsT.</span>

JavaScript

function applySentenceCase() {
    var selector = document.getElementsByClassName('price');
    for( i =0; i<selector.length; i++) {
      var selectorTest = selector[i].innerHTML;
      var replaceText = (selectorTest.charAt(0).toUpperCase() + selectorTest.substr(1).toLowerCase());
      selector[i].innerHTML = replaceText;
    }
}
applySentenceCase();