# var , let & const

# What are variables?

Variables are used to temporarily store values that are needed for a specific purpose in the program. For example, you might use a variable to store the user's name when they enter it into a form, or to keep track of the score in a game.

```javascript
var x = 5; // declare a variable x and assign it the value 5
let y = "Hello"; // declare a variable y and assign it the value "Hello"
const PI = 3.14159; // declare a constant variable PI and assign it the value 3.14159
```

## Difference between var, let & const?

The `var` statement declares a function-scoped or globally-scoped variable, optionally initializing it to a value.

`var` was the original way to declare variables in JavaScript, but it has been largely replaced by `let` and `const` in modern code.

`let` is used to declare a block-scoped variable, which means that the variable is only accessible within the block of code where it was defined. For example:

```javascript
function myFunc(){
    let x = 5 // this x is only accessible within this block of code 
    console.log("x")
}
```

`const` is used to declare a constant variable, which cannot be reassigned to a different value once it has been set. For example:

```javascript
const PI = 3.14159; // PI cannot be reassigned to a different value
```

It's important to note that `const` does not make the value itself unchanging - it only prevents reassignment of the variable. If the value is an object or array, its properties or elements can still be modified.

In general, it's recommended to use `let` and `const` instead of `var`, because they provide more control over variable scoping and help prevent accidental reassignments.

# Template Literal

Template literal is a string literal that allows us to embed expressions inside it using placeholders. These were introduced in ES6 (ECMAScript 2015) and provide a more concise and expressive way of creating strings that contain dynamic values.

```javascript
const name = "Dev";
const age = 23;
const greeting = `Hello, my name is ${name} and I am ${age} years old.`;
console.log(greeting);

// Hello, my name is Dev and I am 23 years old.
```

### Temporal Dead Zone

Temporal Dead Zone is **the period of time during which the let and const declarations cannot be accessed**. Temporal Dead Zone starts when the code execution enters the block which contains the let or const declaration and continues until the declaration has executed.