渐隐渐现fade js

function fadeIn(el){
    el.style.opacity = 0;
    el.style.filter = 'alpha(opacity = 0)';
    el.style.display = 'block';
    var n = 0;
    function fadeShow(){
        if (n < 1){
            n += 0.1;
            el.style.opacity = n;
            el.style.filter = 'alpha(opacity = '+n*100+')';
            var setTimeId = setTimeout(fadeShow, 50);
        }else{
            el.style.opacity = 1;
            el.style.filter = 'alpha(opacity = 100)';
            clearTimeout(setTimeId);
        }
    }
    fadeShow();
}
function fadeOut(el){
    el.style.opacity = 1;
    el.style.filter = 'alpha(opacity = 100)';
    var n = 1;
    function fadeHide(){
        if (n > 0){
            n -= 0.1;
            el.style.opacity = n;
            el.style.filter = 'alpha(opacity = '+n*100+')';
            var setTimeId = setTimeout(fadeHide, 50);
        }else{
            el.style.opacity = 0;
            el.style.filter = 'alpha(opacity = 0)';
            clearTimeout(setTimeId);
            el.style.display = 'none';
        }
    }
    fadeHide();
}