purplebearddan/fictional-octo-fortnight

JS Day 3: Functions

Functions, ES6 and Scope

Lesson Objectives

To Understand...

• Functions
• ES6 Arrow Functions
• Scope

Intros

Functions

In JavaScript, functions are objects that can be invoked to perform a specific task. They can be declared using the function keyword, and can take zero or more parameters as input. Functions can also return a value using the return keyword. Functions in JavaScript are often used for code reuse.

Functions Example

// define a function called "greet"
function greet(name) {
  console.log("Hello, " + name + "!")
}


// "call" the "greet" function 
greet("Alice")
greet("Bob")

Functions Example Output

Hello, Alice!
Hello, Bob!

ES6 Arrow Functions

ES6 introduced arrow functions, which are a shorthand way of writing functions in JavaScript. Arrow functions are anonymous functions that use the => syntax to define the function body. They also have a shorter syntax and an implicit return, which can make them more concise than traditional functions.

Arrow Function Example

const multiply = (x, y) => {
  return x * y;
}

console.log(multiply(2, 3));
console.log(multiply(4, 5));

Arrow Function Example Output

6
20

Scope

Scope refers to the accessibility of variables in different parts of your code. There are two types of scope in JavaScript: global scope and local scope. Variables declared outside of any function have global scope and can be accessed from anywhere in your code. Variables declared inside a function have local scope and can only be accessed within that function.

Scope Example

let globalVar = "I'm a global variable";

function myFunction() {
  let localVar = "I'm a local variable";
  console.log(localVar);
  console.log(globalVar);
}

myFunction();
console.log(globalVar);

Scope Example Output

I'm a local variable
I'm a global variable
I'm a global variable

Resources

W3 Schools

• Functions
• JavaScript Arrow Function
• Scope

MDN Docs

• Functions
• Arrow function expressions
• Scope