JavaScript basics

hello.js

console.log("Hello World!");

// --------------- Variables ---------------

let count = 12;
console.log(count);
count = count + 1;
console.log(count);

const firstName = 'John';
console.log(firstName);
// firstName = 'Jane';
// TypeError: Assignment to constant variable.

// --------------- Strings ---------------

console.log(firstName.length);
console.log(firstName[1]);
console.log(firstName.substring(1, 3));

console.log(firstName.toUpperCase());
console.log(firstName.toLowerCase());

const daysString = 'Mon,Tue,Wedm,Thu,Fri,Sat,Sun'
const days = daysString.split(',')
console.log(days.length)

const first = "Ringo";
const last = "Starr";
const message = `${first} ${last} is a drummer`;
console.log(message);

// --------------- Arrays ---------------

const fruits = [];
fruits.push("Apple");
fruits.push("Orange");
console.log(fruits);

console.log(fruits[0]);
fruits[1] = 'Banana'
console.log(fruits);

fruits.splice(0, 1)
console.log(fruits);

// --------------- Loops ---------------

const beatles = ["paul", "john", "ringo", "george"];
beatles.forEach((beatle) => {
  console.log(beatle.toUpperCase());
});

// --------------- Control flow ---------------

const age = 17;
if (age >= 18) {
  console.log('You can vote');
} else if (age === 17) {
  console.log('You will be able to vote soon');
} else {
  console.log("You can't vote");
}

const number = 12;
if (number !== 0) {
  console.log('number is not zero')
}

const raining = true;
const accessory = raining ? "umbrella" : "sunglasses";

// --------------- Objects ---------------

const student = {
  firstName: 'John',
  lastName: 'Doe'
};

console.log(typeof student);
console.log(student);

console.log(student.firstName);
console.log(student['firstName']);

student.firstName = 'Jane';
student['firstName'] = 'Jane';
console.log(student);

const key = 'age'
student[key] = 40
console.log(student);

// --------------- Functions ---------------

function oldSquare(x) {
  return x * x;
}

const square = (x) => {
  return x * x;
}

// const square = x => x * x;

console.log(oldSquare(5));
console.log(square(5));

// --------------- Function Example ---------------

const capitalize = (str) => {
  // take the first letter
  // uppercase it
  const firstLetter = str[0].toUpperCase();

  // take the rest from the 2nd
  // downcase it
  const restOfTheWord = str.substring(1).toLowerCase();

  // create a new string = first letter + rest of the word
  const result = `${firstLetter}${restOfTheWord}`;

  // return it
  return result;
}

console.log("Result = ", capitalize('waGoN')) // 'Wagon'