嵌套函数中的this

function countDown(){
    var self = this;
    var doWork = function(){
        console.log(this);//window
        console.log(self);//span
    };
    doWork();
};
$(".outer").each(function(index, item){
    countDown.call(this);
})

function countDown(){
    var self = this;
    var doWork = function(){
        console.log(this);//span
        console.log(self);//span
    };
    doWork.call(this);
};
$(".outer").each(function(index, item){
    countDown.call(this);
})

$("#btn1").on("click", function(){
        btn1();//window
    });
    $("#btn2").on("click", btn1);//btn
    function btn1(){
        console.log(this);
    }

function countDown(){
    var timer = null;
    var seconds = $(this).attr("data-seconds");
    var self = this;
    var doWork = function(){
        if(seconds > 0){
            seconds--;
            $(this).html(seconds);
        }else{
            window.clearInterval(timer);
        }
    };
    timer = window.setInterval(function() {
        console.log(this);//window
        doWork.call(self);//改变作用域
    }, 1000);
};
$(".outer").each(function(index, item){
    countDown.call(this);
})