JSFiddle - React, Tailwind, and code Playground

HTML

<form method="POST" id="carForm" action="">
<div class="row-fluid">
    <div class="span2">
        Job:
    </div>
    <div class="span10">
        <select name="car" class="input-block-level">
                <option value="">No car</option>
                <option value="1">Test car</option>
                <option value="2">Test car</option>
                <option value="3">Test car</option>
        </select>
    </div>
</div>
<div class="row-fluid">
    <div class="span2">
        Message:
    </div>
    <div class="span10">
        <textarea name="message" rows="5" id="messageInput" class="input-block-level"></textarea>
    </div>
</div>
<div class="row-fluid">
    <div class="offset2">
        <input type="submit" class="btn btn-primary" id="submitButton" value="Approach" />
    </div>
</div>
</form>

JavaScript

$("#carForm").submit(function(e) {
    var carValue = $(".input-block-level").val();
    
    if (carValue === "") {
        alert("Please select the car");
        $("#alertBox").html("Please add your car before offering buyers");
        $("#alertBox").removeClass('hide');
        e.preventDefault();
        return false;
    }
    
    alert("You have selected a car");
    return false;

});