JavaScript Variables

Source: Dev.to

var

• Old way of declaring variables
• Scope is function‑based (not limited to blocks)
• Can be changed later
• Can be redeclared in the same scope
• Less safe and can lead to unexpected behavior

let

• Modern way to declare variables
• Scope is block‑based
• Value can be changed (reassigned)
• Cannot be redeclared in the same scope
• Safer and more predictable than var

const

• Modern way for fixed values
• Scope is block‑based
• Value cannot be changed or reassigned
• Must be initialized when declared
• Used for values that should stay constant

Scope (where variables exist)

• var → function scope
• let and const → block scope

Hoisting (simple idea)

• var is available before declaration but has an empty value initially
• let and const are also known before declaration but cannot be used before they are defined

JavaScript Modes

Sloppy Mode

• Default mode
• Less strict rules
• Allows unsafe or accidental behaviors

Strict Mode

• Activated manually
• Prevents many common mistakes
• Safer and recommended for real projects