js图片校验

//上传图片
function AjaxFileUpload(url, fileinput) {
    try {
        if (fileinput.files.length <= 0) {
            alert('请选择图片');
            return false;
        }
        var file = fileinput.files[0];
        var re = /^.*?.(jpg|gif|png)$/i;
        if (!re.test(file.name)) {
            alert('未被允许的图片格式');
            return false;
        }
        if (file.size > 1024 * 1024 * 2) {//2M
            $(fileinput).val('');
            alert("图片文件须小于2M");
            return false;
        }
    } catch (err) {
    }
    try {
        validateImageSize(url,fileinput);
    } catch (err) {
        doUpload(url);//也要上传，走后台验证
    }
};
function validateImageSize(url,fileinput) {
    var f = fileinput.files[0];
    var reader = new FileReader();
    reader.onload = function (e) {
        var data = e.target.result;
        //加载图片获取图片真实宽度和高度
        var image = new Image();
        image.onload = function () {
            var width = image.width;
            var height = image.height;
            if (width < 640 || height < 360) {
                $(fileinput).val('');
                alert("尺寸须大于640*360像素！");
                return;
            }
            if (width > 5000 || height > 5000) {
                $(fileinput).val('');
                alert("尺寸须小于5000*5000像素！");
                return;
            }
            doUpload(url);          
        };
        image.src = data;
    };
    reader.readAsDataURL(f);
}
function doUpload(url) {
    $.ajaxFileUpload({
        url: url,
        secureuri: false,
        fileElementId: 'UploadFile',
        dataType: 'json',
        beforeSend: function () {
            $("#loading").show();
        },
        complete: function () {
            $("#loading").hide();
        },
        success: function (data, status) {
            if (data.Result && data.Result.toLowerCase() == "true") {
                $("#showImg").attr("src", data.Message);
                $("#ImageUrl").val(data.Message);
            }
            else
                alert(data.Message);
        },
        error: function (data, status, e) {
            alert(e);
        }
    });
}