Introduction to Morgan.js

15 Dec, 2021
Morgan is a middleware that logs HTTP requests and errors. Middleware is simply a function that has access to the request and response lifecycle methods. We can either use predefined formats or create new ones to format our logs.
Installation of morgan:
Step 1: You can visit morgan for the documentation. The package can be installed with this command.
npm install morgan
Step 2: After the installation is completed you can check the installed version of the package with this command:
npm ls morgan
Step 3: To start working with morgan create a file with the name index.js. The package can be included in the index.js with this command.
const morgan = require('morgan')
Step 4: To use morgan we have to invoke an instance and pass it as an argument to the app.use() which is an express middleware before HTTP requests. This can be done as follows:
app.use(morgan(string));
The string above defines the format in which we want to log our information.
Project Structure: The project structure will look like the below image.
Morgan has five predefined formats that we can use directly to get the required information. These are:
combined:  It gives the Apache standard combined format logs.common: It gives Standard Apache common log output.dev: It is a color-coded log format.short: It is shorter than the default format. It also includes the response time.tiny: It is the shortest log that contains very little information.
combined:  It gives the Apache standard combined format logs.
common: It gives Standard Apache common log output.
dev: It is a color-coded log format.
short: It is shorter than the default format. It also includes the response time.
tiny: It is the shortest log that contains very little information.
The output format of all these predefined formats can be found here.
Example 1:
index.js
// Requiring modulesconst express = require("express");const morgan = require("morgan");const app = express();  // Using combined predefined formatapp.use(morgan("combined"));  // Creating an endpoint where // requests can be made and// we can get logsapp.get("/", (req, res) => {  res.send("GeeksforGeeks");});  // Running on PORTconst PORT = 5000;  app.listen(PORT, () => {  console.log(`Running on PORT: ${PORT}`);});
Step to run the application: In the terminal run the following command to execute the index.js file.
node index.js
Output:
::1 - - [10/Feb/2021:22:18:30 +0000] "GET / HTTP/1.1" 304 - "-" "Mozilla/5.0
(Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) 
Chrome/88.0.4324.150 Safari/537.36"
When you will visit https://localhost:5000 the above log will appear in the console. The log gives us various information like the date and time when the request was made, method of request which is GET in this case, to which URL the request was made which is ‘/’, and much more.
Example 2:
index.js
// Requiring modulesconst express = require("express");const morgan = require("morgan");const app = express();  // Using dev predefined format// Returnsapp.use(morgan("dev"));  // Creating an endpoint where// requests can be made and// we can get logsapp.get("/home", (req, res) => {  res.send("GeeksforGeeks");});  // Running on PORTconst PORT = 5000;  app.listen(PORT, () => {  console.log(`Running on PORT: ${PORT}`);});
Output:
When you visit “https://localhost:5000”, the output will be:
GET / 404 4.031 ms - 139
Since we do not have any endpoint for the “/” URL we end up getting a 404 error with the method of type GET and response time in milliseconds.
When you visit  “https://localhost:5000/home”, the output will be:
GET /home 200 3.416 ms - 13
In our program, we have created an endpoint of “/home” so we get a response of 200 in return.
Example 3:
index.js
// Requiring modulesconst express = require("express");const morgan = require("morgan");const app = express();  // Creating customised logs// :method return method used like - GET,POST// :url returns to which url request was made// :status returns the status returned from req like - 200,404// :response-time returns the time it took to give response// Rest things are printed as it isapp.use(  morgan(    "Method- :method URL- :url Status- :status ResponseTime-  :response-time ms"  ));  // Creating an endpoint where// requests can be made and// we can get logsapp.get("/home", (req, res) => {  res.send("GeeksforGeeks");});  // Running on PORTconst PORT = 5000;  app.listen(PORT, () => {  console.log(`Running on PORT: ${PORT}`);});
Output:
Method- GET URL- /home Status- 200 ResponseTime-  3.392 ms
In the above program, we have customized our output log. The format is : followed by the information name. These are predefined tokens that can be added by using :  in front of them.
We can also create custom tokens with the help of the .token() method. See the below example:
Example 4:
index.js
// Requiring modulesconst express = require("express");const morgan = require("morgan");const app = express();  // Creating custom token// with name timemorgan.token(  "time",  " :method request for :url was received.Response time: :response-time");  // Using the name of// token we created aboveapp.use(morgan("time"));  // Creating an endpoint where// requests can be made and// we can get logsapp.get("/home", (req, res) => {  res.send("GeeksforGeeks");});  // Running on PORTconst PORT = 5000;  app.listen(PORT, () => {  console.log(`Running on PORT: ${PORT}`);});
Output:
GET request for /home was received.Response time: 5.567
Morgan is a very simple logger that allows flexibility when logging HTTP requests and gives us the required information. So this is how we can use morgan in our application
sagar0719kumar
surindertarika1234
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