在onblur函数中使用PHP和Javascript

so I have this form:

所以我有这样的形式:

<form enctype="multipart/form-data" action="cgi-bin/upload.cgi?upload_id=" method="post" onSubmit="return StartUpload(this);" target="xupload">
<table>
    <tr>
        <td class="first"><span class="right">Upload File: </span></td>
        <td class="second"><input name="file_1" type="file" onChange="checkExt(this.value)" accept=".mp4, .avi, .wmv, .mov, .camrec, .flv, .zip, .rar"></td>
        <td class="third"><span class="left">(required)</span></td>
    </tr>
    <tr></tr>
    <tr><center><h2>Video Information</h2></center></tr>
    <tr></tr>
    <tr>
        <td class="first"><span class="right">Your Name: </span></td>
        <td class="second"><input type="text" name="name"></td>
        <td class="third"><span class="left">(preferred)</span></td>
    </tr>
    <tr>
        <td class="first"><span class="right">Series ID: </span></td>
        <td class="second"><input id="series_id" type="text" name="series_id" placeholder="You should have been given this by your admin"></td>
        <td class="third"><span class="left">(preferred)</span></td>
    </tr>
    <tr>
        <td class="first"></td>
        <td class="second"><span id="series_id_check">Enter You're series ID Above and this will change</span></td>
        <td class="third"></td>
    </tr>
    <tr>
        <td class="first"><span class="right">Title: </span></td>
        <td class="second"><input type="text" name="title"></td>
        <td class="third"><span class="left">(preferred)</span></td>
    </tr>
    <tr>
        <td class="first"></td>
        <td class="second center"><small>Please use "<span style="color:#9c0000">&lt;br&gt;</span>" to make a new line</small></td>
        <td class="third"></td>
    </tr>
    <tr>
        <td class="first"><span class="right">Description: </span></td>
        <td class="second"><textarea name="desc"></textarea></td>
        <td class="third"><span class="left">(preferred)</span></td>
    </tr>
    <tr>
        <td class="first"><span class="right">Guests: </span></td>
        <td class="second"><input type="text" name="guests"></td>
        <td class="third"><span class="left">(optional)</span></td>
    </tr>
    <tr>
        <td class="first"><span class="right">Additional Tags: </span></td>
        <td class="second"><input type="text" name="tags"></td>
        <td class="third"><span class="left">(comma separated - optional)</span></td>
    </tr>
</table>
<input type="submit" name="submit" value="Upload File">
</form>
<form encty