How do arrow functions differ from regular functions?

Question

Accepted Answer

Arrow functions are shorter, but the real differences are in **binding behavior**, not just syntax.

```js
const regular = function () {};
const arrow = () => {};
const short = x => x * 2; // implicit return for one expression
```

## The key differences

**1. No own `this`** — arrows inherit `this` from the enclosing scope. This is the most important difference and why they're great for callbacks:

```js
const timer = {
  seconds: 0,
  start() {
    setInterval(() => this.seconds++, 1000); // ✅ `this` is timer
    // a regular function here would have its own `this` (undefined) → bug
  },
};
```

**2. No `arguments` object** — use rest parameters instead:

```js
const sum = (...args) => args.reduce((a, b) => a + b, 0);
```

**3. Cannot be used as constructors** — `new arrow()` throws, and they have no `prototype`.

## When NOT to use an arrow

```js
const obj = {
  name: "Ann",
  greet: () => `Hi ${this.name}`, // ❌ `this` is NOT obj (it's outer scope)
  greet2() { return `Hi ${this.name}`; }, // ✅ method needs dynamic `this`
};
```

Don't use arrows for **object methods** (they won't bind to the object) or when you need a dynamic `this`/`arguments` (event handlers that rely on `this` being the element).

## Why it matters

Use arrows for callbacks and short functions where inheriting `this` is what you want; use regular functions for methods, constructors, and prototype methods.