what is wrong with my http request in javascript?

I want to send a message to the server comprises of a few different sections. The goal is to send some x-www-form-urlencoded info with an image. I tried do sth similiar to this: http://en.wikipedia.org/wiki/MIME#Multipart_messages

This is my js function to do that:

function sendPage() {
    var source = document.getElementById("pageContaine开发者_高级运维r")
    var serializer = new XMLSerializer
    if (!source.hasChildNodes()) {
        alert("nie ma nic do wysłania")
        return
    }
    var DOMNodeInString = "content=" + escape(serializer.serializeToString(source))
    //    sendToServer("savePage.php", true, handleAndShow, DOMNodeInString);return
    xhttp.open("POST", "savePage.php", true)
    var boundary = "xxx"
    var body = "--" + boundary + "\r\n"
    var file = document.getElementById("imgSource").files[0]
    //wysyłam obrazek
    if (file) {
        var reader = new FileReader()
        reader.readAsBinaryString(file)
        body += "Content-Disposition: form-data; name='upload'; filename='" + file.name + "'\r\n"
        body += "Content-Type: application/octet-stream\r\n\r\n"
        body += reader.result + "\r\n"
        body += "--" + boundary + "\r\n"
    }
    //wysyłam pozostałe pola formularza
    body += "Content-Type: multipart/x-www-form-urlencoded \r\n\r\n"
    body += DOMNodeInString
    body += "\r\n--" + boundary + "--"
    xhttp.setRequestHeader("Content-Type", "multipart/mixed; boundary=" + boundary)
    xhttp.onreadystatechange = handleAndShow
    alert(body)
    xhttp.send(body)
}

however, the function doesn't work. My php script is unable to receive $_POST["content"]. What should I change to improve the js script?

It is not possible to upload a file using an XMLHttpRequest. You'll need to use Flash/Java or create a hidden iframe and do an actual submit. I'd suggest using a javascript plugin for "AJAX" file upload.

Apart from @tvanfosson answer, you are missing a creation of the xhttp object:

var xhttp = new XMLHttpRequest();

Use any debugger to see that the JS works without exceptions...