Add a character count below any input field

add_char_limit.js

function setCount(source, target, limit)
{
    var chars = source.val().length;
    if (chars > limit)
    {
        // Disable submit button
        jQuery("input#submit").attr('disabled', 'disabled');
        source.css("background", "#fee");
        target.css("color", "red");
        if ((chars - limit) > 1)
        {
            target.text((chars - limit) + " characters over the limit");
        }
        else
        {
            target.text((chars - limit) + " character over the limit");
        }
    }
    else
    {
        // Enable submit button
        jQuery("input#submit").removeAttr('disabled');
        source.css("background", "white");
        target.css("color", "green");
        target.text(chars + " chars (" + (limit - chars) + " left)");
    }
}

jQuery("#my_source").after(" <span id='my_source_count'></span>");
jQuery("#my_source").on("keyup focus", function()
{
    setCount(jQuery(this), jQuery("#my_source_count"), 600);
});
setCount(jQuery("#my_source"), jQuery("#my_source_count"), 600);