JSFiddle - React, Tailwind, and code Playground

HTML

<form method="post" action="something.html">
    
    <input type="text" id="blah1" class="required" /><br/>
    <input type="text" id="blah2" class="required" /><br/>
    <input type="text" id="blah3" class="required" /><br/>
    <input type="text" id="blah4" class="required" /><br/><br/>
    <a href="#" onclick="insert();">submit</a>
    <button type="submit" onclick="insert();">submit</button>
</form>

JavaScript

function insert() {
        
        var flagInvalid = false;
        var tempArray = document.getElementsByClassName("required");
        for (var i = 0; i < tempArray.length; i++)
        {
            if (tempArray[i].value == ""){
                flagInvalid = true;
                break;
            }
        }

        if (flagInvalid == false) {
            alert ("sending ajax call.");        
        } else {
            alert ("Please enter all required fields.");
        }

    }