头像上传功能实现，PC端的需要做兼容

暂时实现的效果：

http://sandbox.runjs.cn/show/v2vkds3j

<form action="">
    <img id="viewImg" src="photos.png" alt="">
    <input type="file" id="file">
</form>

css:

        #file{
            position: absolute;
            width:;
            height:;
            visibility: hidden;
        }
        #viewImg{
            position:absolute;
            width:200px;
            height:200px;
            border-radius: 100%;
            top:50%;
            left:50%;
            margin-top: -100px;
            margin-left: -100px;
        }

js：哈哈，看你的悟性了。

var view = document.getElementById('viewImg');
        var file = document.getElementById('file');
        $(file).on('change',function(){
            var fileval = this.value;
            if(!/\.(jpg|gif|jpeg|png|bmp)$/ig.test(fileval)){
                alert("图片类型必须是.gif,jpeg,jpg,png,bmp中的一种");
                return false;
            }else{
                var url = window.URL.createObjectURL(file.files[0]);
                view.src = url;
            }
        })
        $(view).on('click',function(){
            $(file).trigger("click");
        })

window.url.createobjecturl 兼容多个浏览器

function setImagePreview() {
var docObj = document.getElementById("ctl00_ContentMain_file_head");
var fileName = docObj.value;
if (!fileName.match(/.jpg|.gif|.png|.bmp/i)) {
alert('您上传的图片格式不正确，请重新选择！');
return false;
} 

var imgObjPreview = document.getElementById("preview");
if (docObj.files && docObj.files[0]) {
//火狐下，直接设img属性
imgObjPreview.style.display = 'block';
imgObjPreview.style.width = '63px';
imgObjPreview.style.height = '63px';
//imgObjPreview.src = docObj.files[0].getAsDataURL();
if (window.navigator.userAgent.indexOf("Chrome") >= 1 || window.navigator.userAgent.indexOf("Safari") >= 1) {
imgObjPreview.src = window.webkitURL.createObjectURL(docObj.files[0]);
}
else {
imgObjPreview.src = window.URL.createObjectURL(docObj.files[0]);
}
} else {
//IE下，使用滤镜
docObj.select();
docObj.blur();
var imgSrc = document.selection.createRange().text;
var localImagId = document.getElementById("localImag");
//必须设置初始大小
localImagId.style.width = "63px";
localImagId.style.height = "63px";
//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;
}