Prefer const and let over var

// ❌ Bad: var leaks out of the block
for (var i = 0; i < 3; i++) {
  setTimeout(() => console.log(i), 100)
}
// Logs: 3, 3, 3 — not 0, 1, 2!
 
// ✅ Good: let is block-scoped
for (let i = 0; i < 3; i++) {
  setTimeout(() => console.log(i), 100)
}
// Logs: 0, 1, 2

// ❌ Bad: var is hoisted and accessible before declaration
console.log(name) // undefined, not ReferenceError
var name = 'Alice'
 
// ✅ Good: let/const throw ReferenceError in the temporal dead zone
console.log(name) // ReferenceError: Cannot access 'name' before initialization
let name = 'Alice'

// ✅ Use const when a binding won't be reassigned
const MAX_RETRIES = 3
const apiUrl = 'https://api.example.com'
const user = fetchUser() // the binding is constant, not the object
 
// ✅ Use let when reassignment is needed
let count = 0
count++
 
let status = 'pending'
status = 'complete'

// ✅ const prevents reassignment of the binding
const user = { name: 'Alice', role: 'admin' }
user.role = 'viewer' // ✅ mutation is allowed
user = { name: 'Bob' } // ❌ TypeError: assignment to constant variable
 
// To make an object truly immutable, use Object.freeze
const config = Object.freeze({ debug: false, version: '1.0' })
config.debug = true // silently fails in sloppy mode, throws in strict mode

{
  "rules": {
    "no-var": "error",
    "prefer-const": "error"
  }
}