如何测试响应是否已设置/发送？

Question

I have the case that a express controller action "may" send contents.

"Send" means either content was send (http 200) or the http status was set to something (http status 204 or a redirect for example)

If nothing was sent/set a default routine should send a default content.

how can i test in my default routine if the express controller action already set contents or set the status code ?

Answer 1

response.headersSent should work.

For example:

if (response.headersSent) {
    console.log('Headers sent!')
} else {
    console.log('Headers have not been sent.')
}
res.writeHead(200);
if (response.headersSent) {
    console.log('Headers sent!')
} else {
    console.log('Headers have not been sent.')
}

Connecting with a client should log:

Headers have not been sent.
Headers sent!