JSFiddle - React, Tailwind, and code Playground

HTML

<div id="div">
    <div class="dv">111</div>
    <div class="dv">111</div>
    <div class="dv">111</div>
    <div class="dv">111</div>
    <div class="dv">111</div>
    <div class="dv">111</div>
    <div class="dv">111</div>
    <div class="dv">111</div>
    <div class="dv">111</div>
</div>

<script type="text/javascript">
    var d = document.getElementsByClassName('dv');
    var div = document.getElementById('div');
    var dv = document.getElementsByClassName('dv');
    var s = d.length;
    var i = 2;

    while (i <= s) {
        var txt = document.createTextNode('555');
        
        dv[i].style.color = 'blue';
        div.insertBefore(txt, dv[i+1]); //добавляем текст перед след. элементом
        
        i += 3;
    }
</script>