[jquery] How to check if text fields are empty on form submit using jQuery?

You can bind an event handler to the "submit" JavaScript event using jQuery .submit method and then get trimmed #log text field value and check if empty of not like:

$('form').submit(function () {

    // Get the Login Name value and trim it
    var name = $.trim($('#log').val());

    // Check if empty of not
    if (name  === '') {
        alert('Text-field is empty.');
        return false;
    }
});

FIDDLE DEMO