Estimation time: 1-4 Days

This is a basic introduction to Node JS and JavaScript.

Learning objectives:

At the end of this learning path, you'll be able to:

• Know basic programming using JavaScript
• Know JavaScript concepts

Send me back home

[[TOC]]

Learning note: all links in this path are reading tutorials. You can read them but you can watch a youtube crash course. if you find useful links, please share them with me.

Here is some examples links:

• MDN web docs
• nodejs official learn

JavaScript is a programming language that is used to create web applications.

Node.js is a JavaScript runtime built on Chrome's V8 JavaScript engine.

In Human words: NodeJS is a program that allows you to run JavaScript on any computer (and not just in the browser). So in order to run JavaScript on your computer, you need to install NodeJS.

NVM (Node.js Version Manager) allows you to quickly install and use different versions of node via the command line.

Even if you only need a single version of Node.js right now, It is still recommend using nvm because it allows you to switch between different versions of Node (depending on the requirements of your project) with minimal hassle.

to install nvm:

curl -o- https://raw.githubusercontent.com/nvm-sh/nvm/v0.39.1/install.sh | bash

Check if node is installed:

nvm --version

For more information you can use the repository nvm-sh/nvm

Optional: zsh plugin with lazy load Or Lazy load nvm for faster shell start. If you follow the setup instructions, you already have this plugin.

You should be familiar with the following concepts:

• Variables
• Operators
• Data types
• Control flow
• Functions
• Objects
• Classes
• Errors
• Modules

Here is some concepts that worth knowing, learn them after you understand the basics:

• Arrays methods - map, filter, reduce etc.
• Spread operator, rest parameters and rest property.
• Pass arguments: call by value, call by sharing, call by reference
• Copy, deep clone, shallow clone.
• this keyword
• bind Function prototype method, and arrow functions vs regular functions binding behavior.
• Higher order functions
• Closures

Some questions about the more advanced topics:

1. • Create a function circlesArea that get array of numbers - each number represent a radius. The function should return the sum of the areas of all circles that their radius is bigger than 0 and their area is smaller than 100. Round the result to the nearest integer.

   For example:

   const radiuses = [-1, 2, 3, 4, 5, 6, 7, 8, 9, 10, -100, 500];
   const sum = circlesArea(radiuses);
   console.log(sum); // 170

   • How many statements did you write in the previous question? If you wrote more than one, refactor the code to use only one line (one statement, you can add new lines for readability).
2. • What is the output of this code?

   const obj = { key: "value" };
   const arr = [...obj];
   console.log(arr);

   • What is the output of this code?

   const arr = [1, 2, 3];
   const obj = { ...arr };
   console.log(obj);

   • What is the output of this code?

   const obj = { ...true, ..."test", ...10 };
   console.log(obj);
   
   const arr = [...true, ..."test", ...10];
   console.log(arr);
   
   const fn = (...args) => args;
   const res = fn(...true, ..."test", ...10);
   console.log(res);

   • Fix this code so it will work as expected:

   const isSummer = false;
   
   const summerFruitsAmount = { watermelon: 30 };
   const fruitsAmount = {
     apple: 10,
     banana: 5,
     ...(isSummer && summerFruits),
   }; // { apple: 10, banana: 5 }
   
   const summerFruits = ["watermelon"];
   const fruits = ["apple", "banana", ...(isSummer && summerFruits)]; // ['apple', 'banana']

3. What is the output of this code? Why?

   function changeNum(num) {
     num = num * 10;
   }
   
   function changeKey(obj) {
     obj.key = "changed";
   }
   
   function changeObj(obj) {
     obj = { key: "changed" };
   }
   
   const num = 10;
   changeNum(num);
   console.log(num);
   
   const obj1 = { key: "unchanged" };
   changeKey(obj1);
   console.log(obj1);
   
   const obj2 = { key: "unchanged" };
   changeObj(obj2);
   console.log(obj2);

4. • What is the output of this code?

   const user = {
     firstName: "Lady",
     lastName: "Gaga",
     address: {
       street: "David king",
       city: "TLV",
       country: "IL",
     },
   };
   
   const copiedUser = { ...user };
   
   copiedUser.firstName = "Jane";
   copiedUser.address.street = "Back street";
   
   console.log(copiedUser);
   console.log(user);

   • Fix the code so there will be no side effects when modifying the copied user.

5. What is the output of this code? Fix the code.

   class LateBloomer {
     #delay;
     petalNumber;
   
     constructor(delay = 1000) {
       this.#delay = delay;
       this.petalNumber = Math.floor(Math.random() * 12) + 1;
     }
   
     bloom() {
       setTimeout(this.declare, this.#delay);
     }
   
     declare() {
       console.log(`I am a beautiful flower with ${this.petalNumber} petals!`);
     }
   }
   
   const flower = new LateBloomer();
   flower.bloom();
   flower.declare();

6. Bonus (optional): Write a function once that accepts a function fn as input and return a new function that is identical to the original function except that it ensures fn is called at most once.

   The first time the returned function is called, it should return the same result as fn. Every subsequent time it is called, it should throw an error with the message "Function already called".

   For example:

   function add(a, b) => a + b;
   
   const addOnce = once(add);
   console.log(addOnce(3, 4)); // 7
   console.log(addOnce(3, 4)); // Error: Function already called
   console.log(addOnce(-2, 8)); // Error: Function already called

Some advanced concepts that worth mentioning, don't learn them now but know that they exist:

• void operator
• Bitwise operators
• Unicode
• Symbols
• Prototypes
• Maps, Sets
• Iterators
• Generators
• WeakMaps, WeakSets
• Typed Arrays
• Proxies

Node.js is an open-source and cross-platform JavaScript runtime environment. Node.js runs the V8 JavaScript engine, the core of Google Chrome, outside of the browser. This allows Node.js to be very performant.

A Node.js app runs in a single process, without creating a new thread for every request. Node.js provides a set of asynchronous I/O primitives in its standard library that prevent JavaScript code from blocking.

Before you continue, make sure you are familiar with the following concepts:

• Package manger (npm)
• package.json, package-lock.json
• File system (node:fs)
• Environment variables (process.env)

1. Write a program that reads a text file and counts the number of words in the file. Accept the file path as argument. The program should output the word count.

   For example, if the input.txt file contains the following text:

     Hello, my cat. And my cat doesn't say "hello" back.
     Hello, my dog. And my dog says "hello" back! 😎

   You should run the program like this:

    node count-words.js input.txt

   The output should be:

   20

   Optional: print the occurrences of each word in the file if the ENV variable DEBUG is set to true.

Some advanced concepts that worth mentioning, don't learn them now but know that they exist:

• Streams
• Buffers
• CJS vs ESM

The internal of node.js:

• v8
• garbage collector
• libuv

Multi-threading:

• Cluster
• Child Processes
• Worker threads
• Thread pools

Additional Topics:

• Asynchronous context tracking
• C/C++ addons

• pnpm
• snyk advisor
• npm audit
• cSpell

Let's get out of sync!