Ajax PHP file upload mistake <p>I have this code in client side: </p> <pre><code>fileUpload: function monkey(){ var file = t.gI("photoFile"); //get element by photoFile var formData = new FormData(); console.log(file.files.length); formData.append("upload", file.files[0]); var req = t.gR(); //XMLHTTPRequest req.open('POST', 'php/fileupload.php', true); req.setRequestHeader("Content-Type", "multipart/form-data", true); req.send(formData); req.onreadystatechange = function () { if (req.readyState === 4) { if (req.status == 200 &amp;&amp; req.status &lt; 300) { t.gI("eventBox").innerHTML = req.responseText; //eventbox error handler adminHandler.eventBox(); } } } }, </code></pre> <p>And this in server side:</p> <pre><code>&lt;?php header('Content-Type:multipart/form-data'); echo $_FILES['upload']['tmp_name']; ?&gt; </code></pre> <p>And I got this error msg: </p> <p>[15-Jun-2015 12:03:21 UTC] PHP Warning: Missing boundary in multipart/form-data POST data in Unknown on line 0 [15-Jun-2015 12:03:21 UTC] PHP Notice: Undefined index: upload in /home/webprogb/public_html/php/fileupload.php on line 4</p> <p>What can I do to fix it? </p>