条件判断を用いた巧みな初期化

   //  checkbox
    var newsletter = $("#newsletter");
    //   checkbox    
    var inital = newsletter.is(":checked");
   //   inital      removeClass addClass  
    var topics = $("#newsletter_topics")[inital ? "removeClass" : "addClass"]("gray");
   //   inital     topics input      
    var topicInputs = topics.find("input").attr("disabled", !inital);
    //  checkbox          
    newsletter.click(function() {
        topics[this.checked ? "removeClass" : "addClass"]("gray");
        topicInputs.attr("disabled", !this.checked);
    });