Variables Explained in Depth - var, let, const

What are Variables?

Variables are containers.

They store information like name, age, score, etc.

Simple idea:

A variable is like a box that stores data.

Why we use Variables?

We use variables to store data so we can use it later.

Examples:

1. Login form (username, password)
2. Show message like "Welcome userName"
3. Game score changes
4. Shopping cart items

First store data, then use it.

Types of Variables

There are 3 types:

1. var (old)
2. let (recommended)
3. const (fixed value)

Basic Difference

1. var and let → value can change
2. const → value cannot change

Example:

Syntax (How to create variable)

1. let → type
2. data → variable name
3. "Anil" → value

Important Rules (Naming)

You can use:

1. letters (a to z)
2. numbers (not at start)
3. underscore (_)
4. dollar ($)

Not allowed:

1. space in name
2. starting with number
3. keywords like var, let, const

Best Practice

1. Use let when value changes
2. Use const when value is fixed
3. Avoid var

Use meaningful names:

Why avoid var?

1. Can declare same variable again
2. Creates confusion
3. Scope issues

Variable Value Change Example

Const Example (Error Case)

Once value is set, it cannot change.

Data Stored in Variables

You can store:

1. name
2. number
3. address
4. any information

Code

What this code does:

1. Creates a variable userName
2. Stores value "anil"
3. Shows alert with "anil"