JSFiddle - React, Tailwind, and code Playground

HTML

<form action="" method="post">
    <label>Login Name:</label><br>
    <input type="text" name="email" id="log" /><br>
    <label>Password:</label><br>
    <input type="text" name="password" id="pwd" /><br>
    <label>Subject:</label><br>
    <input type="text" name="password" id="pwd" /><br>
    <label>Message:</label><br>
    <textarea rows="5" name="message" cols="50" id="message"></textarea><br>
    <input type="submit" name="submit" value="Login" />
</form>

JavaScript

//  Bind the event handler to the "submit" JavaScript event
$('form').submit(function () {
    // return true only if all inputs have text in them, false if otherwise
    return Array.prototype.reduce.call(
        // first argument is the 'this value', we need an array
        // map over the array of inputs, check if empty or not, returns array of trues and falses
        $('input, textarea').map(function(i, x){
            // Check if empty of not
            var text = $.trim($(x).val());
            if (text  == '') {
                alert($(x).attr('name') + ' is empty. All inputs are required.');
                return false;
            } else {
                return true;
            }
        }), 
        // the reduce function, true && false == false
        function(a,b){
            return a && b
        }, 
        // initial value
        true);
});