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README.md

0x05. NodeJS Basics

Back-end JavaScript ES6 NodeJS ExpressJS

82692897e15d9f03256f

Resources

Read or watch:

Requirements

  • Allowed editors: vi, vim, emacs, Visual Studio Code
  • All your files will be interpreted/compiled on Ubuntu 18.04 LTS using node (version 12.x.x)
  • All your files should end with a new line
  • A README.md file, at the root of the folder of the project, is mandatory
  • Your code should use the js extension
  • Your code will be tested using Jest and the command npm run test
  • Your code will be verified against lint using ESLint
  • Your code needs to pass all the tests and lint. You can verify the entire project running npm run full-test
  • All of your functions/classes must be exported by using this format: module.exports = myFunction;

Provided files

database.csv

firstname,lastname,age,field
Johann,Kerbrou,30,CS
Guillaume,Salou,30,SWE
Arielle,Salou,20,CS
Jonathan,Benou,30,CS
Emmanuel,Turlou,40,CS
Guillaume,Plessous,35,CS
Joseph,Crisou,34,SWE
Paul,Schneider,60,SWE
Tommy,Schoul,32,SWE
Katie,Shirou,21,CS

package.json

{
  "name": "node_js_basics",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
  "scripts": {
    "lint": "./node_modules/.bin/eslint",
    "check-lint": "lint [0-9]*.js",
    "test": "./node_modules/mocha/bin/mocha --require babel-register --exit",
    "dev": "nodemon --exec babel-node --presets babel-preset-env ./server.js ./database.csv"
  },
  "author": "",
  "license": "ISC",
  "dependencies": {
    "chai-http": "^4.3.0",
    "express": "^4.17.1"
  },
  "devDependencies": {
    "babel-cli": "^6.26.0",
    "babel-preset-env": "^1.7.0",
    "nodemon": "^2.0.2",
    "eslint": "^6.4.0",
    "eslint-config-airbnb-base": "^14.0.0",
    "eslint-plugin-import": "^2.18.2",
    "eslint-plugin-jest": "^22.17.0",
    "chai": "^4.2.0",
    "mocha": "^6.2.2",
    "request": "^2.88.0",
    "sinon": "^7.5.0"
  }
}

babel.config.js

module.exports = {
  presets: [
    [
      '@babel/preset-env',
      {
        targets: {
          node: 'current',
        },
      },
    ],
  ],
};

.eslintrc.js

module.exports = {
  env: {
    browser: false,
    es6: true,
    jest: true,
  },
  extends: [
    'airbnb-base',
    'plugin:jest/all',
  ],
  globals: {
    Atomics: 'readonly',
    SharedArrayBuffer: 'readonly',
  },
  parserOptions: {
    ecmaVersion: 2018,
    sourceType: 'module',
  },
  plugins: ['jest'],
  rules: {
    'max-classes-per-file': 'off',
    'no-underscore-dangle': 'off',
    'no-console': 'off',
    'no-shadow': 'off',
    'no-restricted-syntax': [
      'error',
      'LabeledStatement',
      'WithStatement',
    ],
  },
  overrides:[
    {
      files: ['*.js'],
      excludedFiles: 'babel.config.js',
    }
  ]
};

and…

Don’t forget to run $ npm install when you have the package.json

Tasks

0. Executing basic javascript with Node JS

In the file 0-console.js, create a function named displayMessage that prints in STDOUT the string argument.

bob@dylan:~$ cat 0-main.js
const displayMessage = require('./0-console');

displayMessage("Hello NodeJS!");

bob@dylan:~$ node 0-main.js
Hello NodeJS!
bob@dylan:~$

1. Using Process stdin

Create a program named 1-stdin.js that will be executed through command line:

  • It should display the message Welcome to Holberton School, what is your name? (followed by a new line)
  • The user should be able to input their name on a new line
  • The program should display Your name is: INPUT
  • When the user ends the program, it should display This important software is now closing (followed by a new line)

Requirements:

  • Your code will be tested through a child process, make sure you have everything you need for that
bob@dylan:~$ node 1-stdin.js 
Welcome to Holberton School, what is your name?
Bob
Your name is: Bob
bob@dylan:~$ 
bob@dylan:~$ echo "John" | node 1-stdin.js 
Welcome to Holberton School, what is your name?
Your name is: John
This important software is now closing
bob@dylan:~$

2. Reading a file synchronously with Node JS

Using the database database.csv (provided in project description), create a function countStudents in the file 2-read_file.js

  • Create a function named countStudents. It should accept a path in argument
  • The script should attempt to read the database file synchronously
  • If the database is not available, it should throw an error with the text Cannot load the database
  • If the database is available, it should log the following message to the console Number of students: NUMBER_OF_STUDENTS
  • It should log the number of students in each field, and the list with the following format: Number of students in FIELD: 6. List: LIST_OF_FIRSTNAMES
  • CSV file can contain empty lines (at the end) - and they are not a valid student!
bob@dylan:~$ cat 2-main_0.js
const countStudents = require('./2-read_file');

countStudents("nope.csv");

bob@dylan:~$ node 2-main_0.js
2-read_file.js:9
    throw new Error('Cannot load the database');
    ^

Error: Cannot load the database
...
bob@dylan:~$
bob@dylan:~$ cat 2-main_1.js
const countStudents = require('./2-read_file');

countStudents("database.csv");

bob@dylan:~$ node 2-main_1.js
Number of students: 10
Number of students in CS: 6. List: Johann, Arielle, Jonathan, Emmanuel, Guillaume, Katie
Number of students in SWE: 4. List: Guillaume, Joseph, Paul, Tommy
bob@dylan:~$

3. Reading a file asynchronously with Node JS

Using the database database.csv (provided in project description), create a function countStudents in the file 3-read_file_async.js

  • Create a function named countStudents. It should accept a path in argument (same as in 2-read_file.js)
  • The script should attempt to read the database file asynchronously
  • The function should return a Promise
  • If the database is not available, it should throw an error with the text Cannot load the database
  • If the database is available, it should log the following message to the console Number of students: NUMBER_OF_STUDENTS
  • It should log the number of students in each field, and the list with the following format: Number of students in FIELD: 6. List: LIST_OF_FIRSTNAMES
  • CSV file can contain empty lines (at the end) - and they are not a valid student!
bob@dylan:~$ cat 3-main_0.js
const countStudents = require('./3-read_file_async');

countStudents("nope.csv")
    .then(() => {
        console.log("Done!");
    })
        .catch((error) => {
        console.log(error);
    });

bob@dylan:~$ node 3-main_0.js
Error: Cannot load the database
...
bob@dylan:~$
bob@dylan:~$ cat 3-main_1.js
const countStudents = require('./3-read_file_async');

countStudents("database.csv")
    .then(() => {
        console.log("Done!");
    })
        .catch((error) => {
        console.log(error);
    });
console.log("After!");

bob@dylan:~$ node 3-main_1.js
After!
Number of students: 10
Number of students in CS: 6. List: Johann, Arielle, Jonathan, Emmanuel, Guillaume, Katie
Number of students in SWE: 4. List: Guillaume, Joseph, Paul, Tommy
Done!
bob@dylan:~$

Tips:

  • Using asynchronous callbacks is the preferred way to write code in Node to avoid blocking threads

4. Create a small HTTP server using Node's HTTP module

In a file named 4-http.js, create a small HTTP server using the http module:

  • It should be assigned to the variable app and this one must be exported
  • HTTP server should listen on port 1245
  • Displays Hello Holberton School! in the page body for any endpoint as plain text

In terminal 1:

bob@dylan:~$ node 4-http.js
...

In terminal 2:

bob@dylan:~$ curl localhost:1245 && echo ""
Hello Holberton School!
bob@dylan:~$ 
bob@dylan:~$ curl localhost:1245/any_endpoint && echo ""
Hello Holberton School!
bob@dylan:~$

5. Create a more complex HTTP server using Node's HTTP module

In a file named 5-http.js, create a small HTTP server using the http module:

  • It should be assigned to the variable app and this one must be exported
  • HTTP server should listen on port 1245
  • It should return plain text
  • When the URL path is /, it should display Hello Holberton School! in the page body
  • When the URL path is /students, it should display This is the list of our students followed by the same content as the file 3-read_file_async.js (with and without the database) - the name of the database must be passed as argument of the file
  • CSV file can contain empty lines (at the end) - and they are not a valid student!

Terminal 1:

bob@dylan:~$ node 5-http.js database.csv
...

In terminal 2:

bob@dylan:~$ curl localhost:1245 && echo ""
Hello Holberton School!
bob@dylan:~$ 
bob@dylan:~$ curl localhost:1245/students && echo ""
This is the list of our students
Number of students: 10
Number of students in CS: 6. List: Johann, Arielle, Jonathan, Emmanuel, Guillaume, Katie
Number of students in SWE: 4. List: Guillaume, Joseph, Paul, Tommy
bob@dylan:~$

6. Create a small HTTP server using Express

Install Express and in a file named 6-http_express.js, create a small HTTP server using Express module:

  • It should be assigned to the variable app and this one must be exported
  • HTTP server should listen on port 1245
  • Displays Hello Holberton School! in the page body for the endpoint /

In terminal 1:

bob@dylan:~$ node 6-http_express.js
...

In terminal 2:

bob@dylan:~$ curl localhost:1245 && echo ""
Hello Holberton School!
bob@dylan:~$ 
bob@dylan:~$ curl localhost:1245/any_endpoint && echo ""
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8">
<title>Error</title>
</head>
<body>
<pre>Cannot GET /lskdlskd</pre>
</body>
</html> 
bob@dylan:~$

7. Create a more complex HTTP server using Express

In a file named 7-http_express.js, recreate the small HTTP server using Express:

  • It should be assigned to the variable app and this one must be exported
  • HTTP server should listen on port 1245
  • It should return plain text
  • When the URL path is /, it should display Hello Holberton School! in the page body
  • When the URL path is /students, it should display This is the list of our students followed by the same content as the file 3-read_file_async.js (with and without the database) - the name of the database must be passed as argument of the file
  • CSV file can contain empty lines (at the end) - and they are not a valid student!

Terminal 1:

bob@dylan:~$ node 7-http_express.js database.csv
...

In terminal 2:

bob@dylan:~$ curl localhost:1245 && echo ""
Hello Holberton School!
bob@dylan:~$ 
bob@dylan:~$ curl localhost:1245/students && echo ""
This is the list of our students
Number of students: 10
Number of students in CS: 6. List: Johann, Arielle, Jonathan, Emmanuel, Guillaume, Katie
Number of students in SWE: 4. List: Guillaume, Joseph, Paul, Tommy
bob@dylan:~$

8. Organize a complex HTTP server using Express

Obviously writing every part of a server within a single file is not sustainable. Let’s create a full server in a directory named full_server.

Since you have used ES6 and Babel in the past projects, let’s use babel-node to allow to use ES6 functions like import or export.

8.1 Organize the structure of the server

  • Create 2 directories within:
    • controllers
    • routes
  • Create a file full_server/utils.js, in the file create a function named readDatabase that accepts a file path as argument:
    • It should read the database asynchronously
    • It should return a promise
    • When the file is not accessible, it should reject the promise with the error
    • When the file can be read, it should return an object of arrays of the firstname of students per fields

8.2 Write the App controller

Inside the file full_server/controllers/AppController.js:

  • Create a class named AppController. Add a static method named getHomepage
  • The method accepts request and response as argument. It returns a 200 status and the message Hello Holberton School!

8.3 Write the Students controller

Inside the file full_server/controllers/StudentsController.js, create a class named StudentsController. Add two static methods:

The first one is getAllStudents:

  • The method accepts request and response as argument
  • It should return a status 200
  • It calls the function readDatabase from the utils file, and display in the page:
    • First line: This is the list of our students
    • And for each field (order by alphabetic order case insensitive), a line that displays the number of students in the field, and the list of first names (ordered by appearance in the database file) with the following format: Number of students in FIELD: 6. List: LIST_OF_FIRSTNAMES
  • If the database is not available, it should return a status 500 and the error message Cannot load the database

The second one is getAllStudentsByMajor:

  • The method accepts request and response as argument
  • It should return a status 200
  • It uses a parameter that the user can pass to the browser major. The major can only be CS or SWE. If the user is passing another parameter, the server should return a 500 and the error Major parameter must be CS or SWE
  • It calls the function readDatabase from the utils file, and display in the page the list of first names for the students (ordered by appearance in the database file) in the specified field List: LIST_OF_FIRSTNAMES_IN_THE_FIELD
  • If the database is not available, it should return a status 500 and the error message Cannot load the database

8.4 Write the routes

Inside the file full_server/routes/index.js:

  • Link the route / to the AppController
  • Link the route /students and /students/:major to the StudentsController

8.5 Write the server reusing everything you created

Inside the file named full_server/server.js, create a small Express server:

  • It should use the routes defined in full_server/routes/index.js
  • It should use the port 1245

8.6 Update package.json (if you are running it from outside the folder full_server)

If you are starting node from outside of the folder full_server, you will have to update the command dev by: nodemon --exec babel-node --presets babel-preset-env ./full_server/server.js ./database.csv

Warning:
  • Don’t forget to export your express app at the end of server.js (export default app;)
  • The database filename is passed as argument of the server.js BUT, for testing purpose, you should retrieve this filename at the execution (when getAllStudents or getAllStudentsByMajor are called for example)

In terminal 1:

bob@dylan:~$ npm run dev
...

In terminal 2:

bob@dylan:~$ curl localhost:1245 && echo ""
Hello Holberton School!
bob@dylan:~$ 
bob@dylan:~$ curl localhost:1245/students && echo ""
This is the list of our students
Number of students in CS: 6. List: Johann, Arielle, Jonathan, Emmanuel, Guillaume, Katie
Number of students in SWE: 4. List: Guillaume, Joseph, Paul, Tommy
bob@dylan:~$ 
bob@dylan:~$ curl localhost:1245/students/SWE && echo ""
List: Guillaume, Joseph, Paul, Tommy
bob@dylan:~$ 
bob@dylan:~$ curl localhost:1245/students/French -vvv && echo ""
*   Trying 127.0.0.1...
* TCP_NODELAY set
* Connected to localhost (127.0.0.1) port 1245 (#0)
> GET /students/SWES HTTP/1.1
> Host: localhost:1245
> User-Agent: curl/7.58.0
> Accept: */*
>
< HTTP/1.1 500 Internal Server Error
< X-Powered-By: Express
< Date: Mon, 06 Jul 2020 03:29:00 GMT
< Connection: keep-alive
< Content-Length: 33
<
* Connection #0 to host localhost left intact
Major parameter must be CS or SWE
bob@dylan:~$

If you want to add test to validate your integration, you will need to add this file: .babelrc

{
    "presets": [["env", {"exclude": ["transform-regenerator"]}]]
}