Boxes for Data

A variable is just a name (label) attached to a memory area where data is stored.

1. const — Your Best Friend

Use const for everything you don't plan to change. This guarantees you won't accidentally overwrite important data.

const API_URL = 'https://api.site.com';

2. let — When Data Changes

Use let if the value will be updated (like a score counter in a game).

let score = 0;
score = score + 10;

3. The Death of var

var is an archaism. It has weird scoping: it ignores { ... } blocks (e.g., inside an if).

4. How to Name Variables?

• Use camelCase (firstWordSmall, OthersCapitalized).
• Names must be descriptive: userName is better than un.
• Constants known in advance (before code execution) are often written in UPPER_CASE.