Express.js res.headersSent Property - GeeksforGeeks

08 Jul, 2020
The res.headersSent property is a boolean property that indicates if the app sent HTTP headers for the response.
Syntax:
res.headersSent
Parameter: No parameters.
Return Value: This property returns a Boolean value either True or False.
Installation of express module:
You can visit the link to Install express module. You can install this package by using this command.npm install expressAfter installing the express module, you can check your express version in command prompt using the command.npm version expressAfter that, you can just create a folder and add a file for example, index.js. To run this file you need to run the following command.node index.js
You can visit the link to Install express module. You can install this package by using this command.npm install express
npm install express
After installing the express module, you can check your express version in command prompt using the command.npm version express
npm version express
After that, you can just create a folder and add a file for example, index.js. To run this file you need to run the following command.node index.js
node index.js
Example 1: Filename: index.js
var express = require('express');var app = express(); var PORT = 3000;  app.get('/', function (req, res) {      // Before res.send()     console.log(res.headersSent);     res.send('OK');});  app.listen(PORT, function(err){    if (err) console.log(err);    console.log("Server listening on PORT", PORT);});
Steps to run the program:
The project structure will look like this:Make sure you have installed express module using the following command:npm install expressRun index.js file using below command:node index.jsOutput:Server listening on PORT 3000
Now open your browser and go to http://localhost:3000/, now you can see the following output on your console:Server listening on PORT 3000
false

The project structure will look like this:
Make sure you have installed express module using the following command:npm install express
npm install express
Run index.js file using below command:node index.jsOutput:Server listening on PORT 3000

node index.js
Output:
Server listening on PORT 3000

Now open your browser and go to http://localhost:3000/, now you can see the following output on your console:Server listening on PORT 3000
false

Server listening on PORT 3000
false

Example 2: Filename: index.js
var express = require('express');var app = express(); var PORT = 3000;  app.get('/', function (req, res) {    res.send('OK');      // After res.send()     console.log(res.headersSent); });  app.listen(PORT, function(err){    if (err) console.log(err);    console.log("Server listening on PORT", PORT);});
Run index.js file using below command:
node index.js
Output:Now open your browser and make GET request to http://localhost:3000, now you can see the following output on your console:
Server listening on PORT 3000
true

Reference: https://expressjs.com/en/4x/api.html#res.headersSent
Express.js
Node.js
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