المتغيرات و الكائنات في جافا اسكريبت | الجزء الثاني

المتغيرات و الكائنات في جافا اسكريبت | الجزء الثاني

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3.1 Variables and Data Types

Variables are used to store and manipulate data in JavaScript. Here are the key concepts related to variables and data types:

3.1.1 Variable Declaration and Assignment

– Use the `let` keyword to declare a variable that can be reassigned later.

– Use the `const` keyword to declare a constant variable that cannot be reassigned.

– Example:

javascript

let name = “John”;

const age = 25;

3.1.2 Data Types

JavaScript has several built-in data types, including:

– Numbers: Numeric values, such as `3`, `3.14`, or `1000`.

– Strings: Textual values enclosed in quotes, such as `”Hello”` or `’World’`.

– Booleans: Logical values `true` or `false`.

– Arrays: Ordered lists of values, enclosed in square brackets, such as `[1, 2, 3]`.

– Objects: Key-value pairs enclosed in curly brackets, such as `{ name: “John”, age: 25 }`.

– Null: Represents the absence of any object value.

– Undefined: Represents an uninitialized variable.

3.2 Operators and Expressions

Operators allow you to perform operations on variables and values. Here are some commonly used operators:

3.2.1 Arithmetic Operators

– Addition: `+`

– Subtraction: `-`

– Multiplication: `*`

– Division: `/`

– Modulus (Remainder): `%`

– Example:

javascript

let x = 10;

let y = 5;

let sum = x + y; // 15

let product = x * y; // 50

3.2.2 Comparison Operators

– Equal to: `==`

– Not equal to: `!=`

– Greater than: `>`

– Less than: `<`

– Greater than or equal to: `>=`

– Less than or equal to: `<=`

– Example:

javascript

let a = 10;

let b = 5;

console.log(a > b); // true

console.log(a == b); // false

3.2.3 Logical Operators

– AND: `&&`

– OR: `||`

– NOT: `!`

– Example:

javascript

let sunny = true;

let warm = true;

console.log(sunny && warm); // true

console.log(sunny || warm); // true

console.log(!sunny); // false

3.3 Control Flow and Conditional Statements

Conditional statements allow you to control the flow of execution based on certain conditions. Here are two commonly used conditional statements:

3.3.1 If Statement

– Executes a block of code if a specified condition is true.

– Example:

javascript

let hour = 12;

if (hour < 12) {

console.log(“Good morning!”);

} else {

console.log(“Good afternoon!”);

}

3.3.2 Switch Statement

– Evaluates an expression and executes different code blocks based on different cases.

– Example:

javascript

let day = “Monday”;

switch (day) {

case “Monday”:

console.log(“Start of the week”);

break;

case “Friday”:

console.log(“End of the week”);

break;

default:

console.log(“Some other day”);

}

3.4 Functions

Functions allow you to group and reuse blocks of code. Here’s an example of defining and calling a function:

javascript

function greet(name) {

console.log(“Hello, ” + name + “!”);

}

greet(“John”); // Hello, John!

3.5 Arrays and Objects

Arrays and objects are used to store and manipulate collections of data.

3.5.1 Arrays

– Arrays store multiple values in a single variable.

– Example:

javascript

let numbers = [1, 2, 3, 4];

console.log(numbers[0]); // 1

3.5.2 Objects

– Objects store key-value pairs.

– Example:

javascript

let person = {

name: “John”,

age: 25,

city: “New York”

};

console.log(person.name); // John

Summary:

– Variables are used to store and manipulate data in JavaScript.

– JavaScript has various data types, including numbers, strings, booleans, arrays, and objects.

– Operators and expressions allow you to perform operations on variables and values.

– Conditional statements like `if` and `switch` control the flow of execution based on conditions.

– Functions allow you to group and reuse blocks of code.

– Arrays and objects are used to store and manipulate collections of data.

Homework:

– Practice writing JavaScript code that uses variables, data types, operators, conditional statements, and functions.

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