Express: res.headersSent: Check whether response headers send to the client or not

res.headersSent

This property used to check whether response headers are sent to the client or not.

index.js

'use strict'

const express = require('express')

const app = express()

app.get('/', (req, res) => {
 console.log(`Is headers sent ? : ${res.headersSent}`)
 res.send('Hello World')
 console.log(`Is headers sent ? : ${res.headersSent}`)
})

const port = 3000
app.listen(port, () => console.log(`Application started listening on port ${port}!`));

Run index.js

Open the url ‘http://localhost:3000/’ in browser, you can see below messages in console.

Is headers sent ? : false

Is headers sent ? : true

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