Course source code: https://codistwa.com/guides/functions. More courses on https://codistwa.com

functions.js

// ============================================================
// Without parameter
// ============================================================
  
function double () {
  console.log('Hello world')
}

console.log(double()) // Hello world

// ============================================================
// One parameter
// ============================================================

function double (x) {
  return x * 2;
}

const square = (x) => x ** 2;

console.log(double(4)); // 8
console.log(square(4)); // 16

// ============================================================
// Two parameters
// ============================================================

const ids = (firstName, lastName) => 
  `My name is ${firstName} ${lastName}`;

console.log(ids('Mickael', 'Jackson'));

// ============================================================
// Scope
// ============================================================

const apple = 3;

const getApple = (apple) => apple - 2;

console.log(getApple(30)); // 28

// ============================================================
// Optional, default
// ============================================================

const id2 = (firstName, age = 30) => {
  if (firstName) {
    return `My name is ${firstName} and I have ${age} years old`;
  } 
  return `I have ${age} years old`;
}

console.log(id2('Francis')); // My name is Francis and I have 30 years old
console.log(id2()); // I have 30 years old

functions.py

# ============================================================
# Without parameter
# ============================================================

def double():
    print('Hello world')

print(double())  # Hello world

# ============================================================
# One parameter
# ============================================================

def double(x):
    return x * 2

def square(x):
    return x ** 2

print(double(4))  # 8
print(square(4))  # 16

# ============================================================
# Two parameters
# ============================================================

def ids(first_name, last_name):
    return f'My name is {first_name} {last_name}'

print(ids('Mickael', 'Jackson'))

# ============================================================
# Scope
# ============================================================

apple = 3

def get_apple(apple):
    return apple - 2

print(get_apple(30))  # 28

# ============================================================
# Optional, default
# ============================================================

def id2(first_name='', age=30):
    if first_name:
        return f'My name is {first_name} and I have {age} years old'
    return f'I have {age} years old'


print(id2('Francis'))  # My name is Francis and I have 30 years old
print(id2())  # I have 30 years old