Good practices to declare variables

General rule: Prefer non-reassignable, local scope, variables

True for every language

1. Use by default const if possible
2. Use let if you need to re-assigned the variable
3. Avoid var (outdated, too large scope)
- Use only if you really need function scope

Rem.

- const and let introduced in EC6
- Many internet code still use the outdated var from previous JS