Functions

---

// Defining the function:
function sum(num1, num2) {
  return num1 + num2;
}
 
// Calling the function:
console.log(sum(3, 6)); // 9
 

Anonymous Functions

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// Named function
function rocketToMars() {
  return 'BOOM!';
}
 
// Anonymous function
const rocketToMars = function () {
  return 'BOOM!';
};

Arrow Functions

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With no arguments

const printHello = () => {
	console.log('hello');
};
printHello(); // => hello

With arguments

const sum = (param1, param2) => {
	return param1 + param2;
};
console.log(sum(2, 5)); // => 7

Concise arrow functions

const multiply = (a, b) => a * b;
console.log(multiply(2, 30)); // => 60

return Keyword

---

// With return
function sum(num1, num2) {
  return num1 + num2;
}
 
// The function doesn't output the sum
function sum(num1, num2) {
  num1 + num2;
}

Functions Assigned to Variables

---

let plusFive = (number) => {
  return number + 5;
};
let f = plusFive; // f is assigned the value of plusFive
plusFive(3); // 8
// Since f has a function value, it can be invoked.
f(5); // 10

Callback Functions

---

const isEven = (n) => {
  return n % 2 == 0;
};
 
let printMsg = (evenFunc, num) => {
  const isNumEven = evenFunc(num);
  console.log(`${num} is an even number: ${isNumEven}.`);
};
 
// Pass in isEven as the callback function
printMsg(isEven, 4);
// => 4 is an even number: True.