If you've spent too much time in jQuery you might not realize that streaming is supported by the underlying XMLHttpRequest object. The readyState property can be set to LOADING or DONE. Most applications will wait for DONE so they have a complete document to work with. A "normal" payload will be small enough that the lag between LOADING and DONE is tiny, but a big download can definitely be parsed as it loads. Imagine an HTML doc with inline JavaScript. That JavsScript is evaluated as soon as it's encountered and doesn't wait for a page load that may never happen.