JavaScript 치트 시트

// => Hello world!
console.log("Hello world!");

// => Hello CheatSheets.zip
console.warn("hello %s", "CheatSheets.zip");

// Output error message to standard error
console.error(new Error("Oops!"));

let amount = 6;
let price = 4.99;

let x = null;
let name = "Tammy";
const found = false;

// => Tammy, false, null
console.log(name, found, x);

var a;
console.log(a); // => undefined

let single = "Wheres my bandit hat?";
let double = "Wheres my bandit hat?";

// => 21
console.log(single.length);

5 + 5 = 10     // Addition
10 - 5 = 5     // Subtraction
5 * 10 = 50    // Multiplication
10 / 5 = 2     // Division
10 % 5 = 0     // Modulus

// This is a comment

/*
You need to change this setting
before deployment.
*/

let number = 100;

// Both statements add 10
number = number + 10;
number += 10;

console.log(number);
// => 120

let age = 7;

// String concatenation
"Tommy is " + age + " years old.";

// String interpolation
`Tommy is ${age} years old.`;

const isMailSent = true;

if (isMailSent) {
  console.log("Mail sent to recipient");
}

var x = 1;

// => true
result = x == 1 ? true : false;

true || false; // true
10 > 5 || 10 > 20; // true
false || false; // false
10 > 100 || 10 > 20; // false

1 > 3; // false
3 > 1; // true
250 >= 250; // true
1 === 1; // true
1 === 2; // false
1 === "1"; // false

const fruits = ["apple", "orange", "banana"];

// Different data types
const data = [1, "chicken", false];

const apple = {
  color: "Green",
  price: { bulk: "$3/kg", smallQty: "$4/kg" },
};
console.log(apple.color); // => Green
console.log(apple.price.bulk); // => $3/kg

class Dog {
  constructor(name) {
    this._name = name;
  }

  introduce() {
    console.log("This is " + this._name + " !");
  }

  // Static method
  static bark() {
    console.log("Woof!");
  }
}

const myDog = new Dog("Buster");
myDog.introduce();

// Calling static method
Dog.bark();

// myMath.js

// Default export
export default function add(x, y) {
  return x + y;
}

// Named export
export function subtract(x, y) {
  return x - y;
}

// Multiple exports
function multiply(x, y) {
  return x * y;
}
function duplicate(x) {
  return x * 2;
}
export { multiply, duplicate };

function helloWorld() {
  return new Promise((resolve) => {
    setTimeout(() => {
      resolve("Hello World!");
    }, 2000);
  });
}

async function msg() {
  const msg = await helloWorld();
  console.log("Message:", msg);
}

msg(); // Message: Hello World! <-- after 2 seconds