# JavaScript: Variables

* In JavaScript, variables are containers for storing data values. They are declared using '***var',' let'***, or '***const'*** keywords and can hold various types of information such as numbers, strings, or objects.
    
* In JavaScript, variables can be implicitly declared without using keywords like '***const', 'let',*** or ***'var'***, but doing so may lead to unintended consequences and is generally discouraged for clarity and best coding practices.
    

**Syntax:** *<mark>keyword variableName = value</mark>*

```javascript
const jersey=10;
let name="messi";
var  team="MLS@10";
team="Argentina"
```

### ***const*** & ***let***

* Variables declared with ***'let'*** and ***'const'*** are block-scoped
    
* Block scope refers to the visibility of variables within curly braces {}.
    
* They are only accessible within the block where they are defined.
    
    ```javascript
    function variables(){
    let name="sam";
    const age=24;
    }
    console.log(name,age) //ReferenceError: name is not defined
    ```
    

# **Constant**\*: <mark>const</mark>\*

* It retains a fixed value throughout its scope and cannot be reassigned,
    
* It provides a stable reference to unchanging data.
    
    ```javascript
    const name="sajid"
    name="hussain"
    console.log(name);
    //TypeError: Assignment to constant variable.
    ```
    

# ***let***

* After initializing a variable with '***let'*** its value can be altered by assigning a different value.
    
* It allows flexibility in data manipulation.
    
    ```javascript
    let name="sajid"
    name="hussain"
    console.log(name);
    //output - hussain
    ```
    
    # Undefined
    
* undefined variable is one that has been declared but not assigned a value.
    
* Accessing or using such a variable will result in an 'undefined' value.
    
    ```javascript
    let car;
    console.log(car); //undefined
    ```