Functions

3 Ways to Create Functions in JavaScript
There are three ways to create functions in JavaScript:

1.Plain or Normal Function
2.Function Expression (function without a name stored in a variable)
3.Arrow Function (can be written in implicit or explicit style and can return objects)

1. Normal Function

function sayMyName() {   // `()` inside is called parameters
  console.log("Sam");
}

sayMyName;   // This is a reference to the function, but it does NOT run it
sayMyName(); // This calls the function and runs it

// Output: Sam

1. Function Expression This is a function without a name stored in a variable.

const showNum = function(a) {
  return a;
}

console.log(showNum(5)); // Output: 5
console.log(showNum());  // Output: undefined, because no argument was passed

1. Arrow Function Arrow functions can be written in two ways: a) Implicit Return (no need to write return keyword)

const addNum = (a, b) => a + b;
console.log(addNum(2, 3)); // Output: 5
console.log(addNum());      // Output: NaN (because no arguments passed)

You can also use parentheses for returning an object:

const addNumTwo = (a, b) => (a + b);
console.log(addNumTwo(3, 4)); // Output: 7

b) Explicit Return (use return keyword inside braces)

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

const result = addNumOne(2, 3);
console.log(result); // Output: 5

Arrow Function Returning Objects
You can use arrow functions to return objects like this:

const result = (str) => ({ length: str.length, uppercase: str.toUpperCase() });
console.log(result("hello")); 
// Output: { length: 5, uppercase: "HELLO" }

const analyzeSentence = sentence => ({ wordCount: sentence.split(" ").length });
console.log(analyzeSentence("JavaScript is fun"));
// Output: { wordCount: 3 }

const calculateSquareAndCube = (num) => ({ square: num ** 2, cube: num ** 3 });
console.log(calculateSquareAndCube(4));
// Output: { square: 16, cube: 64 }

More Arrow Function Examples (with explicit return)

Sum of Array Elements
const arr = [1, 2, 3, 4, 5];
const sumOfArr = (arr) => {
  let sum = 0;
  for (let i = 0; i < arr.length; i++) {
    sum += arr[i];
  }
  return sum;
}

console.log(sumOfArr(arr)); // Output: 15

Reverse a String

const reverse = (str) => {
  let rev = "";
  for (let i = str.length - 1; i >= 0; i--) {
    rev += str[i];
  }
  return rev;
}

console.log(reverse("hello")); // Output: olleh