js判断是否绑定click事件

function showPreviousPeriodHistory(){
    num += 12;
    displayFusionHistoryLineBlock(num);
    var $events = $._data($(".fusionHistorypageContainer .next")[0],"events");
    if(!($events && $events["click"])){
        $(".fusionHistorypageContainer .next").css("color","#4286de");
        $(".fusionHistorypageContainer .next").click(showNextPeriodHistory);
    }
    if(num/12>=5){
        $(".fusionHistorypageContainer .previous").css("color","#a6a6a6");
        $(".fusionHistorypageContainer .previous").unbind("click");
    }
}

function showNextPeriodHistory(){
    num -= 12;
    displayFusionHistoryLineBlock(num);
    var $events = $._data($(".fusionHistorypageContainer .previous")[0],"events");
    if(!($events && $events["click"])){
        $(".fusionHistorypageContainer .previous").css("color","#4286de");
        $(".fusionHistorypageContainer .previous").click(showPreviousPeriodHistory);
    }
    if(num < 12){
        $(".fusionHistorypageContainer .next").css("color","#a6a6a6");
        $(".fusionHistorypageContainer .next").unbind("click");
    }
}