JavaScript variables are containers for data.
Variables = Data Containers
JavaScript Variables can be declared in 4 ways:
OLD Javascript:
- Automatically
- Using var
Modern Javascript:
- Using let
- Using const
| Feature | var | let | const |
| Introduced In | Old JavaScript | ES6 (Modern JS) | ES6 (Modern JS) |
| Scope | Function Scope | Block Scope | Block Scope |
| Can Reassign Value? | Yes | Yes | No |
| Can Redeclare Variable? | Yes | No | No |
| Default Value Before Declaration | undefined | Temporal Dead Zone | Temporal Dead Zone |
| Used For | Old code | Changing values | Fixed values |
| Preferred in Modern JS | No | Yes | Yes |
| Example | var age = 20; | let age = 20; | const PI = 3.14; |