Create Session11.md

Frontend-dev/Session11.md

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+### JavaScript Functions
+
+#### 1. **Introduction to Functions**
+   - **Definition**: Functions are reusable blocks of code designed to perform a specific task. They help in reducing code repetition.
+   - **Syntax**:
+     ```javascript
+     function functionName(parameters) {
+       // Code to be executed
+     }
+     ```
+   - **Example**:
+     ```javascript
+     function greet(name) {
+       console.log("Hello, " + name + "!");
+     }
+     greet("Alice");
+     ```
+
+#### 2. **Function Expressions**
+   - **Definition**: Functions can also be defined as expressions and assigned to variables.
+   - **Syntax**:
+     ```javascript
+     const functionName = function(parameters) {
+       // Code to be executed
+     };
+     ```
+   - **Example**:
+     ```javascript
+     const greet = function(name) {
+       console.log("Hello, " + name + "!");
+     };
+     greet("Bob");
+     ```
+
+#### 3. **Arrow Functions**
+   - **Definition**: A shorter syntax for writing function expressions, introduced in ES6.
+   - **Syntax**:
+     ```javascript
+     const functionName = (parameters) => {
+       // Code to be executed
+     };
+     ```
+   - **Example**:
+     ```javascript
+     const greet = (name) => {
+       console.log("Hello, " + name + "!");
+     };
+     greet("Charlie");
+     ```
+
+#### 4. **Function Parameters and Arguments**
+   - **Parameters**: Variables listed as part of the function definition.
+   - **Arguments**: Values passed to the function when it is invoked.
+   - **Default Parameters**: Functions can have default parameter values if no arguments are provided.
+     ```javascript
+     function greet(name = "Stranger") {
+       console.log("Hello, " + name + "!");
+     }
+     greet(); // Output: Hello, Stranger!
+     ```
+
+#### 5. **Return Statement**
+   - **Definition**: Functions can return a value using the `return` statement. The function execution stops when the `return` statement is reached.
+   - **Example**:
+     ```javascript
+     function add(a, b) {
+       return a + b;
+     }
+     const result = add(5, 3); // result = 8
+     ```
+
+### Callback Functions
+
+#### 1. **Definition**
+   - A callback function is a function passed as an argument to another function and is executed after the completion of that function.
+   - **Example**:
+     ```javascript
+     function greet(name, callback) {
+       console.log("Hello, " + name);
+       callback();
+     }
+
+     function sayGoodbye() {
+       console.log("Goodbye!");
+     }
+
+     greet("Alice", sayGoodbye); // Output: Hello, Alice \n Goodbye!
+     ```
+
+#### 2. **Asynchronous Callback**
+   - Callbacks are often used in asynchronous operations, such as reading files, making network requests, or setting timers.
+   - **Example**:
+     ```javascript
+     setTimeout(() => {
+       console.log("This runs after 2 seconds");
+     }, 2000);
+     ```
+
+### Array Functions
+
+#### 1. **map()**
+   - **Definition**: The `map()` method creates a new array by applying a function to each element of an array.
+   - **Syntax**:
+     ```javascript
+     const newArray = array.map(function(currentValue, index, arr), thisValue);
+     ```
+   - **Example**:
+     ```javascript
+     const numbers = [1, 2, 3, 4];
+     const squares = numbers.map(number => number * number);
+     console.log(squares); // [1, 4, 9, 16]
+     ```
+
+#### 2. **filter()**
+   - **Definition**: The `filter()` method creates a new array containing elements that pass a test provided by a function.
+   - **Syntax**:
+     ```javascript
+     const newArray = array.filter(function(currentValue, index, arr), thisValue);
+     ```
+   - **Example**:
+     ```javascript
+     const numbers = [1, 2, 3, 4, 5];
+     const evenNumbers = numbers.filter(number => number % 2 === 0);
+     console.log(evenNumbers); // [2, 4]
+     ```
+
+#### 3. **reduce()**
+   - **Definition**: The `reduce()` method executes a reducer function on each element of the array, resulting in a single output value.
+   - **Syntax**:
+     ```javascript
+     const result = array.reduce(function(accumulator, currentValue, index, arr), initialValue);
+     ```
+   - **Example**:
+     ```javascript
+     const numbers = [1, 2, 3, 4];
+     const sum = numbers.reduce((total, number) => total + number, 0);
+     console.log(sum); // 10
+     ```
+