JSFiddle - React, Tailwind, and code Playground

HTML

<html>
<head>
    <title>Form</title>
</head>
<body>
<h1>Form</h1>
<form name="Entry" method="post" action="">
    <table width="50%" border="0">
        <tr>
            <td id="name">Name</td>
            <td><input type="text" name="name"/></td>
        </tr>
        <tr>
            <td id="subject">Age</td>
            <td><input type="text" name="age" id="age" /></td>
        </tr>
        <tr>
            <td id=”number”>Number</td>
            <td><input type="text" name="number" id="number"/></td>
        </tr>

        <tr>
            <td><button onclick="validateForm();" id="submit_btn" type="button" name="Submit" value="Submit">Submit</button></td>
            <td><input type="reset" name="Reset" value="Reset" /></td>

        </tr>
    </table>
</form>


<script type="text/javascript">
    //Assuring page is loaded
    document.onload = function(){
        validateForm();
    };

    var validateForm = function() {
        var result = true;
        var msg="";
        var name,age,number;


        name  = document.getElementsByName("name")[0];
        age  = document.getElementsByName("age")[0];
        number  = document.getElementsByName("number")[0];

        //Conditionals
        if (name.value =="") {
            msg+="You must enter your name \n";
            name.focus();
            name.style.color="red";
            result = false;
        }
        if (age.value=="") {
            msg+="You must enter your age \n";
            age.focus();
            age.style.color="red";
            result = false;
        }
        if (number.value=="") {
            msg+="You must enter your number \n";
            number.focus();
            number.style.color="red";
            result = false;
        }

        if(msg==""){
            return result;
        }

        {
            alert(msg);
            return result;
        }

    };
</script>
</body>
</html>