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: 0;
            height: 0;
            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; 
}