Arrow Functions

Arrow functions in Node.js are a concise way to write functions. They are great for short, single-expression functions and have unique behaviors like lexical this binding. However, they lack their own this, arguments object, and can't be used as constructors with new.

1. Basic Syntax

const add = (a, b) => a + b;

2. Single Parameter

const greet = name => `Hello, ${name}`;

No need for parentheses if there’s only one parameter.

3. No Parameters

const sayHello = () => 'Hello!';

Use empty parentheses when there are no parameters.

4. Implicit Return

const double = x => x * 2;

No need for return or curly braces for single expression functions.

5. Block Body

const sum = (a, b) => {
    const result = a + b;
    return result;
};

Use curly braces when you need multiple statements.

6. Lexical this

const obj = {
    name: 'Node.js',
    getName: () => this.name
};
console.log(obj.getName()); // Outputs: undefined (depends on surrounding scope)

Arrow functions don’t have their own this; they inherit this from the surrounding context.

7. No arguments Object

const add = () => {
    console.log(arguments); // `arguments` is not defined
};

Arrow functions don’t have their own arguments object.

8. No new Keyword

const Person = (name) => {
    this.name = name;
};
const john = new Person('John'); // Error: Person is not a constructor

Arrow functions can’t be used as constructors.

9. No Prototype

const ArrowFunc = () => {};
console.log(ArrowFunc.prototype); // Outputs: undefined

Arrow functions don’t have a prototype property, so they can’t be used to define methods on a prototype.

10. Arrow Functions in Callbacks

setTimeout(() => console.log('Executed after 1 second'), 1000);

Often used in callbacks for their concise syntax and lexical this binding, especially in asynchronous operations.

11. Empty Arrow Function

// An empty arrow function returns undefined
const empty = () => {};

(() => "foobar")();
// Returns "foobar"
// (this is an Immediately Invoked Function Expression)

12. Promise

promise
  .then((a) => {
    // …
  })
  .then((b) => {
    // …
  });

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