https://developer.mozilla.org/zh-CN/docs/AJAX
https://developer.mozilla.org/zh-CN/docs/AJAX/Getting_Started
https://developer.mozilla.org/zh-CN/docs/Web/API/XMLHttpRequest
https://developer.mozilla.org/zh-CN/docs/Web/API/XMLHttpRequest/Using_XMLHttpRequest
https://developer.mozilla.org/zh-CN/docs/Web/API/GlobalFetch/fetch
https://developer.mozilla.org/zh-CN/docs/Web/API/Worker
https://developer.mozilla.org/zh-CN/docs/Server-sent_events/Using_server-sent_events
blob to string
http://stackoverflow.com/a/23024613
https://stackoverflow.com/questions/23024460/javascript-i-created-a-blob-from-a-string-how-do-i-get-the-string-back-out
http://qnimate.com/an-introduction-to-javascript-blobs-and-file-interface/