图片上传之前预览

//使用JS
<script>
//下面用于多图片上传预览功能
function setImagePreviews(avalue) {
var docObj = document.getElementById("doc");
var dd = document.getElementById("showImg");
dd.innerHTML = "";
var fileList = docObj.files;
for (var i = 0; i < fileList.length; i++) {
dd.innerHTML += "<img id='img" + i + "'  /> ";
var imgObjPreview = document.getElementById("img"+i);
if (docObj.files && docObj.files[i]) {
//火狐下，直接设img属性
imgObjPreview.style.display = 'block';
//imgObjPreview.style.width = '150px';
//imgObjPreview.style.height = '180px';
//imgObjPreview.src = docObj.files[0].getAsDataURL();
//火狐7以上版本不能用上面的getAsDataURL()方式获取，需要一下方式
imgObjPreview.src = window.URL.createObjectURL(docObj.files[i]);
}
else {
//IE下，使用滤镜
docObj.select();
var imgSrc = document.selection.createRange().text;
alert(imgSrc)
var localImagId = document.getElementById("img" + i);
//必须设置初始大小
localImagId.style.width = "150px";
localImagId.style.height = "180px";
//图片异常的捕捉，防止用户修改后缀来伪造图片
try {
localImagId.style.filter = "progid:DXImageTransform.Microsoft.AlphaImageLoader(sizingMethod=scale)";
localImagId.filters.item("DXImageTransform.Microsoft.AlphaImageLoader").src = imgSrc;
}
catch (e) {
alert("您上传的图片格式不正确，请重新选择!");
return false;
}
imgObjPreview.style.display = 'none';
document.selection.empty();
}
}
return true;
}
</script>

<script>
//下面用于多图片上传预览功能
function setImagePreviews(avalue) {
var docObj = document.getElementById("doc");
var dd = document.getElementById("showImg");
dd.innerHTML = "";
var fileList = docObj.files;
for (var i = 0; i < fileList.length; i++) {
dd.innerHTML += "<img id='img" + i + "'  /> ";
var imgObjPreview = document.getElementById("img"+i);
imgObjPreview.style.display = 'block';
imgObjPreview.src = window.URL.createObjectURL(docObj.files[i]);
}
return true;
}
</script>

$(function(){
$('.try').change(function(e){
var obj = $(this).parents(".choose-img").find(".preview");
var file = e.target.files[0];
preview(file , obj);
});
})
function preview(file , obj){
var img = new Image();
url = img.src=URL.createObjectURL(file);
var $img = $(img);
img.onload = function(e){
URL.revokeObjectURL(url);
obj.empty().append($img);
}
/*当banner点击上传图片的时候*/
$(".cho-img-upload").on("click",function  () {
$(".ban-bg-img img").attr("src", URL.createObjectURL(file));
$(".choose-img").hide();
})

}