Express.js res.append() Function

The res.append() function appends the specified value to the HTTP response header field and if the header is not already set then it creates the header with the specified value.

Syntax:

res.append(field [, value])

Parameter: The field parameter describes the name of the field that need to be appended and the value parameter can be a string or an array.

Returns: It retuns an Object.

Installation of express module:



  1. You can visit the link to Install express module. You can install this package by using this command.
    npm install express
  2. After installing the express module, you can check your express version in command prompt using the command.
    npm version express
  3. 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

Example 1: Filename: index.js

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var express = require('express');
var app = express();
var PORT = 3000;
  
// Without middleware
app.get('/', function(req, res){
    res.append('Warning', '201 Warning');
    console.log(res.get('Warning')); // 201 Warning
});
  
app.listen(PORT, function(err){
    if (err) console.log(err);
    console.log("Server listening on PORT", PORT);
});

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Steps to run the program:

  1. The project structure will look like this:
  2. Make sure you have installed express module using the following command:
    npm install express
  3. Run index.js file using below command:
    node index.js

    Output:

    Server listening on PORT 3000
    
  4. Open your browser and go to http://localhost:3000/, now you see the following output on your console:
    Server listening on PORT 3000
    201 Warning
    

Example 2: Filename: index.js

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var express = require('express');
var app = express();
var PORT = 3000;
  
// With middleware
app.use('/', function(req, res, next){
    res.append('Warning', '201 Its a Warning');
    next();
})
  
app.get('/', function(req, res){
    console.log(res.get('Warning')); 
    res.send();
});
  
app.listen(PORT, function(err){
    if (err) console.log(err);
    console.log("Server listening on PORT", PORT);
});

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Run index.js file using below command:

node index.js

Now, open the browser and go to http://localhost:3000/, now check your console and you will see the following output:

Server listening on PORT 3000
201 Its a Warning

Reference: https://expressjs.com/en/5x/api.html#res.append




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