Javascript

The fundamentals according to the common base

• Variables: Declaration / assignment / scope
• Data types: String / Number / Boolean / Array / Object / Null / Undefined / Symbol / bigInt
• Operator: Arithmetic / Assignment / Comparison / Logic / Bitwise
• Conditional: If / Else / Switch
• Loop: For / While / Do While / For In / For Of
• Function: Declaration / Expression / Arrow / Callback

Variables

Declaration variables

let name;

Assignment variables

name = "ATC";

combo

let name = "ATC";
  

Variable scope

The scope of a variable is the area of ​​code in which it can be accessed.

In JavaScript, variables can be declared in 4 different ways, each with a different scope:

var

Medium pre ES6, Variables declared with var are global. This means they are accessible everywhere in your code. Var variables can be redeclared or updated at any time. (not recommended)

let and const

These declarations are block-scoped, meaning they are limited to the blocks in which they are defined.

If you declare a variable with let or const inside a for loop, for example, it will not be accessible outside of that loop.

/!\ const (for constant) cannot be reassigned, let if.

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Data Types

One of the most fundamental aspects of programming is understanding data types. In JavaScript, each value belongs to a specific data type.

String

• Description: Sequences of characters used to represent text.

let phrase = "phrase totalement random";

Number

• Description: Represents both integers and floating point numbers.

let age = 25;
let prix = 19.99;

Boolean

• Description: Represents a true (true) or false (false) value.

let estMajeur = true;

Array

• Description: Structures used to store multiple values ​​in a single variable.

let fruits = ["pomme", "banane", "cerise"];

Object

• Description: Collections of properties, represented by a key and a value.

let voiture = {
  marque: "Toyota",
  modèle: "Corolla",
  année: 2020,
};

Null

• Description: Represents the intentional absence of value.

let data = null;

Undefined

• Description: An uninitialized variable has the value undefined.

let test;
console.log(test); // Affiche "undefined"

Symbol

• Description: A unique, immutable data type.

const sym1 = Symbol("description");

bigInt

• Description: Allows you to represent integers larger than 2^53 - 1.

const bigNumber = 1234567890123456789012345678901234567890n;

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Operators

Operators perform actions on variables and values. They are the essential tools for manipulating data.

Arithmetic:

• Example: +, -, *, /, %

Assignment:

• Example: =, +=, -=, *=, /=

Comparison:

• Example: ==, ===, !=, !==, >, <, >=, <=

Logic:

• Example: &&, ||, !

Bitwise:

• Example: &, |, ^, ~, <<, >>, >>>

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** Conditional Structures**

Conditional structures allow you to execute blocks of code based on certain conditions.

If

     if (condition) {
       // code à exécuter si la condition est vraie
    }
  

Else

     if (condition) {
       // code si la condition est vraie
     } else {
       // code si la condition est fausse
     }
  

Switch

     switch (expression) {
       case x:
         // code à exécuter si expression === x
         break;
       case y:
         // code à exécuter si expression === y
         break;
       default:
       // code à exécuter si expression ne correspond à aucune case
     }
  

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Curls

Loops are used to repeatedly execute a block of code.

For

     for (initialisation; condition; mise à jour) {
       // code à répéter
     }
  

While

     while (condition) {
       // code à répéter tant que la condition est vraie
     }
  

Do While

     do {
       // code à répéter
     } while (condition);
  

For In

  for (let cle in objet) {
    // code pour chaque propriété de l'objet
  }

For Of

     for (let element of iterable) {
       // code pour chaque élément de l'itérable (e.g., array)
     }
  

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Functions

Functions are blocks of code designed to perform a specific task.

Statement

     function nomDeLaFonction(parametres) {
       // corps de la fonction
     }
  

Expression

     const maFonction = function (parametres) {
       // corps de la fonction
     };
  

Arrow

     const maFonction = (parametres) => {
       // corps de la fonction
     };
  

Callback

• Description: A function passed as an argument to another function to be executed after the latter has finished.

     function saluer(callback) {
       console.log("Bonjour");
       callback();
     }

     saluer(function () {
       console.log("Au revoir");
     });
  

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