图片预加载

function preloadimages(arr){
var newimages=[], loadedimages=0
var arr=(typeof arr!="object")? [arr] : arr
function imageloadpost(){
loadedimages++
if (loadedimages==arr.length){
alert("图片已经加载完成")
}
}
for (var i=0; i<arr.length; i++){
newimages[i]=new Image()
newimages[i].src=arr[i]
newimages[i].onload=function(){
imageloadpost()
}
newimages[i].onerror=function(){
imageloadpost()
}
}
}