图片上传前预览

<div style="border:2px dashed red;">
            <p>
                图片上传前预览：<input type="file" id="xdaTanFileImg" onchange="xmTanUploadImg(this)" accept="image/*"/>
                <input type="button" value="隐藏图片" onclick="document.getElementById('xmTanImg').style.display = 'none';"/>
                <input type="button" value="显示图片" onclick="document.getElementById('xmTanImg').style.display = 'block';"/>
            </p>
            <img id="xmTanImg"/>
            <div id="xmTanDiv"></div>
        </div>
        <hr />
        <script type="text/javascript">            
            //判断浏览器是否支持FileReader接口
            if (typeof FileReader == 'undefined') {
                document.getElementById("xmTanDiv").InnerHTML = "<h1>当前浏览器不支持FileReader接口</h1>";
                //使选择控件不可操作
                document.getElementById("xdaTanFileImg").setAttribute("disabled", "disabled");
            }

            //选择图片，马上预览
            function xmTanUploadImg(obj) {
                var file = obj.files[0];
                
                console.log(obj);console.log(file);
                console.log("file.size = " + file.size);  //file.size 单位为byte

                var reader = new FileReader();

                //读取文件过程方法
                reader.onloadstart = function (e) {
                    console.log("开始读取....");
                }
                reader.onprogress = function (e) {
                    console.log("正在读取中....");
                }
                reader.onabort = function (e) {
                    console.log("中断读取....");
                }
                reader.onerror = function (e) {
                    console.log("读取异常....");
                }
                reader.onload = function (e) {
                    console.log("成功读取....");

                    var img = document.getElementById("xmTanImg");
                    img.src = e.target.result;
                    //或者 img.src = this.result;  //e.target == this
                }

                reader.readAsDataURL(file)
            }
        </script>

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