js上传图片，并预览

<div id="divID"></div>
    <input name="uplBase_Student_Learn_ProvePicURL1" id="uplBase_Student_Learn_ProvePicURL1" type="file" onchange="previewImage(this, 'divID')"
        value="上传学位证" />

 //显示图片
        function previewImage(file, showId) {
            try {
                filename = file.value;
                var fileText = filename.substring(filename.lastIndexOf("."), filename.length); //获取文件扩展名
                fileText = fileText.toLowerCase();

                if (window.ActiveXObject)//判断条件也可以改为navigator.userAgent.indexOf("MSIE")!=-1
                {
                    //IE浏览器
                    var image = new Image();
                    image.dynsrc = file.value;
                    if (image.fileSize > (1048576 * 5)) {
                        file.value = "";
                        alert("文件大小不可大于5M！");
                        return false;
                    }
                }
                else {
                    var filePath = file.value;
                    var fileExt = filePath.substring(filePath.lastIndexOf(".")).toLowerCase();
                    if (file.files[0].size > (1048576 * 5)) {
                        file.value = "";
                        alert("文件大小不可大于5M！");
                        return false;
                    }
                }
            } catch (e) {
            }
            var MAXWIDTH = 72;
            var MAXHEIGHT = 73;
            var div = document.getElementById("divID");
            div.innerHTML = '<img id=img_' + showId + '>';
            var img = document.getElementById('img_' + showId);
            img.onload = function () {
                img.width = 72;
                img.height = 73;
            }
            var reader = new FileReader();
            reader.onload = function (evt) { img.src = evt.target.result; }
            reader.readAsDataURL(file.files[0]);
        }