JSFiddle - React, Tailwind, and code Playground

HTML

<form action="#" id="contact">
    <input type="text" class="req"><br>
    <input type="text" class="req"><br>
    <input type="text" class="req"><br>
    <textarea name="" id="" cols="30" rows="10" class="req"></textarea><br>
    <input type="submit">
                    
</form>

JavaScript

document.getElementById('contact').onsubmit = function() {
	var children = this.children;
    var arr = Array.prototype.slice.call(children )
    
	for(var i = 0, l= arr.length; i < l; i++) {
		if (children[i].className == 'req') {
			
			alert(arr[i]); //defined
			alert(l); //undefined

		}
	}


	return false;
};