d3.request()

d3.request(url[, callback])

Returns a new asynchronous request for specified url. If no callback is specified, the request is not yet sent and can be further configured. If a callback is specified, it is equivalent to calling request.get immediately after construction:

d3.request(url)
    .get(callback);

Note: if you wish to specify a request header or a mime type, you must not specify a callback to the constructor. Use request.header or request.mimeType followed by request.get instead.