Get the response length of a Koa response body, streams in particular.
byteLength is added to
If a non-stream body is set,
this is the
If a stream body is set,
this is the current amount of bytes sent to the response.
To find the total amount of bytes sent,
byteLength property after the response emits the
You may also use it as a function, though it's still a generator even though it's not async.
var byteLength =app