使用jquery,FormData对象实现文件上传和loading效果

    <!-- 文件选择框 -->
    <input type="file" id="file1">

    <!-- 上传按钮 -->
    <button id="btnUpload">上传</button>

    <img src="../images/loading.gif" alt="" style="display: none;" id="img">


    <script>
        $(document).ajaxStart(function () {
            $('#img').show();
        })

        $(document).ajaxStop(function () {
            $('#img').hide();
        })
        $('#btnUpload').on('click', function () {
            // console.log('1');
            var files = $('#file1')[0].files;
            console.log(files);
            if (files.length <= 0) {
                return alert('请选择文件后在上传！')
            }

            var fd = new FormData();
            fd.append('avatar', files[0])

            $.ajax({
                type: 'POST',
                url: 'http://www.liulongbin.top:3006/api/upload/avatar',
                data: fd,
                contentType: false,
                processData: false,
                success(res) {
                    console.log(res);
                }
            })
        })
    </script>