JSFiddle - React, Tailwind, and code Playground

HTML

<form action="check.php" method="POST" id="userform" onSubmit="return passCheck()" >
    USERNAME:<input name="uname" type="text" />
    PASSWORD:<input type="password" id="upass" name="upass" type="text" />
    RETYPE PASSWORD:<input type="password" id="reupass" name="reupass" type="text" />
    <input type="submit" value="Submit" >
</form>

JavaScript

function passCheck(){
    var pass1 = document.getElementById('upass').value;
    var pass2 = document.getElementById('reupass').value;
    if(pass1 == pass2 && pass1 != ""){
        return true;
    }
    else{
        alert("Both password inputs do not match. Please retry.");
        document.getElementById('userform').reset();
        return false;
    }
}