我是一名经验丰富的程序员,但我正在尝试学习JavaScript,并且通过了解事情的工作方式来学习最佳。我发现一个脚本可以淡化数组中的图像。这是脚本document.getElementById的值是什么?
window.addEventListener?window.addEventListener("load",so_init,false):window.attachEvent("onload",so_init);
var d=document, imgs = new Array(), zInterval = null, current=0, pause=false;
function so_init() {
if(!d.getElementById || !d.createElement)return;
css = d.createElement("link");
css.setAttribute("href","xfade2.css");
css.setAttribute("rel","stylesheet");
css.setAttribute("type","text/css");
d.getElementsByTagName("head")[0].appendChild(css);
imgs = d.getElementById("imageContainer").getElementsByTagName("img");
for(i=1;i<imgs.length;i++) imgs[i].xOpacity = 0;
imgs[0].style.display = "block";
imgs[0].xOpacity = .99;
setTimeout(so_xfade,1000);
}
function so_xfade() {
cOpacity = imgs[current].xOpacity;
nIndex = imgs[current+1]?current+1:0;
nOpacity = imgs[nIndex].xOpacity;
cOpacity-=.05;
nOpacity+=.05;
imgs[nIndex].style.display = "block";
imgs[current].xOpacity = cOpacity;
imgs[nIndex].xOpacity = nOpacity;
setOpacity(imgs[current]);
setOpacity(imgs[nIndex]);
if(cOpacity<=0) {
imgs[current].style.display = "none";
current = nIndex;
setTimeout(so_xfade,1000);
} else {
setTimeout(so_xfade,50);
}
function setOpacity(obj) {
if(obj.xOpacity>.99) {
obj.xOpacity = .99;
return;
}
obj.style.opacity = obj.xOpacity;
obj.style.MozOpacity = obj.xOpacity;
obj.style.filter = "alpha(opacity=" + (obj.xOpacity*100) + ")";
}
}
我有困难的部分是与这些线路
window.addEventListener?window.addEventListener("load",so_init,false):window.attachEvent("onload",so_init);
和
if(!d.getElementById || !d.createElement)return;
一切我能找到同时显示了window.addEventListener和d.getElementById是窗口和文档对象的方法分别。那么当他们被调出没有任何参数时,他们的价值是什么?在这些情况下,什么样的条件会使他们真实,什么样的条件会使他们失实。
好神。什么浏览器不支持'getElementById'? IE4? – ThinkingStiff 2012-01-04 23:02:07
@ThinkingStiff:是的:)。它是在IE 5中实现的。我不知道何时执行'createElement',所以我留下了我的评论,现在它一直受到支持。 – 2012-01-04 23:03:03