JavaScript 備忘錄

Hey everyone! I've got some great news for all you beginners learning JavaScript! A quick reference guide for JavaScript is now available! You can easily check important concepts, functions, and methods right away. For more details about the guide, check it out here.

What's in the Quick Reference Guide

Console

// => 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!"));

Numbers

let amount = 6;
let price = 4.99;

Variables

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

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

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

Strings

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

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

Arithmetic Operators

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

Comments

// This is a comment

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

Assignment Operators

let number = 100;

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

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

String Interpolation

let age = 7;

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

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

Conditional Statements

const isMailSent = true;

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

Ternary Operator

var x = 1;

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

Logical Operators

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

Comparison Operators

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

Arrays

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

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

Objects

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

Classes

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();

Modules

// 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 };

Asynchronous Processing

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

This quick reference guide covers a wide range of topics from the basics to more advanced JavaScript concepts. Be sure to download it here and make it a handy tool for your coding journey!

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