js判断文件类型大小并给出提示

　　　　　　<form id="uploadForm" method="post" class="layui-form">
            <div class="layui-form-item">
                <label class="layui-form-label">名称</label>
                <div class="layui-input-block">
                    <input type="text" name="name" required lay-verify="required"
                        placeholder="请输入文件名" autocomplete="off" class="layui-input">
                </div>
            </div>

            <div class="layui-form-item">
                <label class="layui-form-label">资料类型:</label>
                <div class="layui-input-block">
                    <select name="datatypeid"  id="datatypeid"></select>
                </div>
                <input type="hidden" id="yincang">
            </div>
            <div class="layui-form-item">
                <label class="layui-form-label">上传文件</label>

                <div class="layui-input-block">
                    <input class="layui-input" type="file" name="file" onchange="fileChange(this);"/>
                </div>
            </div>

            <div class="layui-form-item">
                <div class="layui-input-block">

                    <input type="button" class="layui-btn" value="上传"
                        onclick="upload()" />
                </div>
            </div>
        </form>

    <script type="text/javascript">
        var isIE = /msie/i.test(navigator.userAgent) && !window.opera;
        function fileChange(target, id) {
            var fileSize = 0;
            var filetypes = [  ".doc", ".docx" ];//这里设置接受的文件类型
            var filepath = target.value;
            var filemaxsize = 1024 * 10;//接受的文件最大10M 
            if (filepath) {
                var isnext = false;
                var fileend = filepath.substring(filepath.indexOf("."));
                if (filetypes && filetypes.length > 0) {
                    for (var i = 0; i < filetypes.length; i++) {
                        if (filetypes[i] == fileend) {
                            isnext = true;
                            break;
                        }
                    }
                }
                if (!isnext) {
                    alert("不接受此文件类型！");
                    target.value = "";
                    return false;
                }
            } else {
                return false;
            }
            if (isIE && !target.files) {
                var filePath = target.value;
                var fileSystem = new ActiveXObject("Scripting.FileSystemObject");
                if (!fileSystem.FileExists(filePath)) {
                    alert("附件不存在，请重新输入！");
                    return false;
                }
                var file = fileSystem.GetFile(filePath);
                fileSize = file.Size;
            } else {
                fileSize = target.files[0].size;
            }

            var size = fileSize / 1024;
            if (size > filemaxsize) {
                alert("附件大小不能大于" + filemaxsize / 1024 + "M！");
                target.value = "";
                return false;
            }
            if (size <= 0) {
                alert("附件大小不能为0M！");
                target.value = "";
                return false;
            }
        }
    </script>