Submit ajax request with file upload via JavaScript

Question

I have a form that can be submitted via form.submit() and the response is correct. Now I want to submit it using ajax, but I have a problem when submitting a file.

The form is pretty simple:

<form name="Upload" enctype="multipart/form-data" method="post" action="upload.asp">
    <input type="file" name="file" id="fileinput"/>
    <input type="button" name="FileUpload" class="button" id="append_new" 
    onclick="xmlhttpPost('upload.asp', document.getElementById('fileinput').files[0]);" value="submit file"/>
</form>

I got the ajax call as following:

function xmlhttpPost(strURL, form) {
    var xmlHttpReq = false;
    var self = this;
    // Mozilla/Safari
    if (window.XMLHttpRequest) {
        self.xmlHttpReq = new XMLHttpRequest();
    }
    // IE
    else if (window.ActiveXObject) {
        self.xmlHttpReq = new ActiveXObject("Microsoft.XMLHTTP");
    }
    self.xmlHttpReq.open('POST', strURL, true);
    self.xmlHttpReq.setRequestHeader('Content-Type', 'multipart/form-data');
    self.xmlHttpReq.onreadystatechange = function() {
        if (self.xmlHttpReq.readyState == 4) {
            updatepage(self.xmlHttpReq.responseText);
        }
    }
    self.xmlHttpReq.send('file=' + file);
}

function updatepage(str){
    document.getElementById("fileitems").innerHTML = str;
}

The problem now is: the server gets the string [object file] rather than the actual file content. How can I make sure file data is submitted?

Answer 1

You can use formData for that:

function xmlhttpPost(strURL, form) {
    var xmlHttpReq = false;
    var self = this;
    // Mozilla/Safari
    if (window.XMLHttpRequest) {
        self.xmlHttpReq = new XMLHttpRequest();
    }
    // IE
    else if (window.ActiveXObject) {
        self.xmlHttpReq = new ActiveXObject("Microsoft.XMLHTTP");
    }
    self.xmlHttpReq.open('POST', strURL, true);
    self.xmlHttpReq.setRequestHeader('Content-Type', 'multipart/form-data');
    self.xmlHttpReq.onreadystatechange = function () {
        if (self.xmlHttpReq.readyState == 4) {
            updatepage(self.xmlHttpReq.responseText);
        }
    }
    if ( !! window.FormData) {
        var formData = new FormData();
        formData.append('file', form);
        self.xmlHttpReq.send(formData);
    }
}

function updatepage(str) {
    document.getElementById("fileitems").innerHTML = str;
}

Here's a decent example of a full ajax file uploader with progress.

Answer 2

You are missing this:

self.xmlHttpReq.setRequestHeader("X_FILENAME", file.name);

That will differentiate between a normal POST and a file upload for the app tier.

If you are using PHP, it would look something like:

$file = (isset($_SERVER['HTTP_X_FILENAME']) ? $_SERVER['HTTP_X_FILENAME'] : '');