Express.js - How to check if headers have already been sent?

user_312483 0
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I am writing a library which may set headers. I want to give a custom error message if headers have already been sent, instead of just letting it fail with the "Can't set headers after they are sent" message given by Node.js. So how to check if headers have already been sent?

response-headers express node.js javascript
3 Answers

Others answers point to Node.js or Github websites.

Below is from Expressjs website: https://expressjs.com/en/api.html#res.headersSent

app.get('/', function (req, res) {
  console.log(res.headersSent); // false
  res.send('OK');
  console.log(res.headersSent); // true
});
user_9844710
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