I get the form page through Ajax.
The following is the form code:

    <form  method="post" enctype="multipart/form-data" class="form-horizontal">
        <p class="form-group" style="margin-left:0px;">
            <label for="file">注：选择头像文件尽量小于2M</label>
            <input id="headPortraitFile" type="file" name="portrait"> 
        </p>
        <button id="headPortraitSubmit" type="button" class="btn-sm btn-primary">上传头像</button>
    </form>

But the input type="file" in this form cannot directly select the file in the browser, let alone submit the file. Do not know what is the reasons of that? I haven't been able to solve it in the past two days. Please ask for help! ! !