# Filter(),Map(),Reduce() in Javascript.

---

### Filter:

* **Definition:** The `filter()` method creates a shallow copy of a portion of an array, based on a provided function.
    
* **Example 1:**
    
    ```javascript
    const words = ['spray', 'elite', 'exuberant', 'destruction', 'present'];
    const result = words.filter((word) => word.length > 6);
    // Output: ["exuberant", "destruction", "present"]
    ```
    
* **Example 2:**
    
    ```javascript
    const myNums = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
    const newNums = myNums.filter((num) => num > 4);
    // Output: [5, 6, 7, 8, 9, 10]
    ```
    
* **Common Mistake:**
    
    ```javascript
    // Incorrect code
    const newNums = myNums.filter((num) => {
      num > 4;
    });
    // Output: []
    // Correction: Missing return statement
    ```
    

### Map:

* **Definition:** The `map()` method creates a new array by applying a function to each element of the original array.
    
* **Example:**
    
    ```javascript
    const myNumbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
    const newNumsMap = myNumbers.map((num) => num + 10);
    // Output: [11, 12, 13, 14, 15, 16, 17, 18, 19, 20]
    ```
    
* **Chaining Map and Filter:**
    
    ```javascript
    const chainedResult = myNumbers
      .map((num) => num * 10)
      .map((num) => num + 1)
      .filter((num) => num >= 40);
    ```
    

### Reduce:

* **Definition:** The `reduce()` method executes a user-supplied "reducer" callback function on each element of an array.
    
* **Basic Example:**
    
    ```javascript
    const array1 = [1, 2, 3, 4];
    const initialValue = 0;
    const sumWithInitial = array1.reduce(
      (accumulator, currentValue) => accumulator + currentValue,
      initialValue,
    );
    // Output: 10
    ```
    
* **Reduce with Array of Objects:**
    
    ```javascript
    const shoppingCart = [
      { itemName: "js cource", price: 2999 },
      { itemName: "py cource", price: 999 },
      { itemName: "c++ cource", price: 9999 },
      { itemName: "data science cource", price: 12999 },
    ];
    
    const priceToPay = shoppingCart.reduce((acc, item) => acc + item.price, 0);
    // Output: Sum of all prices in the shopping cart
    ```
    

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