Welcome to JavaScript!

Hello! Here you are going to find my personal cheatsheet for JavaScript! Few free to use and adapt this codes for your own needs. You can easily start a new vanilla JS project with Vite.

Declaring Variables

To declare our variables, we can use let for variables that can change and const for variables that are constant.

let changeableVariable = "Lucas"
const nonChangeableVariable = 3.14

Loops

We can iterate through things using both our basic for and while instructions.

for (let index = 0; index < array.length; index++) {
  const element = array[index]
}

while (condition) {}

Declaring Functions and different types of functions

Here, we have 3 types of declaration:

Our basic and classic function
Arrow function (which is a more compact way of declaring a function)
and Anonymous Function (which is a way to declare a function without a name)

//classic function
function showMessage(message) {
  console.log(message)
}
//arrow function
const alsoShowsMessage = (message) => console.log(message)


//anonymous functions (same use as the arrow function, but with different syntax)
(function () {
  console.log("Oi escondido!");  // I will invoke myself
})();

//you can check more about functions here: 
//https://www.w3schools.com/js/js_function_definition.asp

showMessage("Oi")
alsoShowsMessage("Oi de novo!")

Working with Arrays

We have a lot of methods that can help us with arrays. A few of them are:

push
pop()
forEach()
map()

You can see more methods here.

//working with arrays
// using const because this is always going to be an array
const ourAmazingArray = [1, 2, 3, 4, 5]

//accessing one array position
console.log(ourAmazingArray[2])

// iterating through array
ourAmazingArray.forEach((value) => console.log(value))
const ourNewAmazingArray = ourAmazingArray.map((value) => value)

//adding to the end of the array
ourAmazingArray.push(6)

console.log(ourAmazingArray, ourNewAmazingArray)

//removing the last item from the array
ourAmazingArray.pop()

console.log(ourAmazingArray, ourNewAmazingArray)

Interpolating values into strings

Here is an example of how we can insert the content from a variable inside some string.

const ourAmazingArray = [1, 2, 3, 4, 5]

const showElement = (element, position) =>
  console.log(`The element ${element} is on position ${position}`)

ourAmazingArray.map(showElement)

Working with JSON

Here is a few examples of working with JSON.

const ourAmazingJsonArray = [
  {
    userId: 1,
    id: 1,
    title:
      "sunt aut facere repellat provident occaecati excepturi optio reprehenderit",
    body: "quia et suscipit\nsuscipit recusandae consequuntur expedita et cum\nreprehenderit molestiae ut ut quas totam\nnostrum rerum est autem sunt rem eveniet architecto"
  },
  {
    userId: 1,
    id: 2,
    title: "qui est esse",
    body: "est rerum tempore vitae\nsequi sint nihil reprehenderit dolor beatae ea dolores neque\nfugiat blanditiis voluptate porro vel nihil molestiae ut reiciendis\nqui aperiam non debitis possimus qui neque nisi nulla"
  },
  {
    userId: 1,
    id: 3,
    title: "ea molestias quasi exercitationem repellat qui ipsa sit aut",
    body: "et iusto sed quo iure\nvoluptatem occaecati omnis eligendi aut ad\nvoluptatem doloribus vel accusantium quis pariatur\nmolestiae porro eius odio et labore et velit aut"
  },
  {
    userId: 1,
    id: 4,
    title: "eum et est occaecati",
    body: "ullam et saepe reiciendis voluptatem adipisci\nsit amet autem assumenda provident rerum culpa\nquis hic commodi nesciunt rem tenetur doloremque ipsam iure\nquis sunt voluptatem rerum illo velit"
  }
]
//show titles
const showTitle = (obj) => console.log(obj.title)

ourAmazingJsonArray.map(showTitle)

//filter out titles which length is greater than 20
const filterLongTitles = (obj) => obj.title.length < 20

console.log(ourAmazingJsonArray.filter(filterLongTitles))

OOP in JS

Here we have one basic Rectangle class, in which we declare our width and height, in order to create Rectangle instances in the future.

class Rectangle {
  constructor(width, height) {
    this.width = width
    this.height = height
  }

  showValues() {
    console.log(this.width, this.height)
  }

  calculateArea() {
    console.log(this.width * this.height)
  }
}

const myRectangle = new Rectangle(10, 20)
myRectangle.showValues()
myRectangle.calculateArea()

Working with an API

We can use the fetch method to fetch an API response and then work with the response data.

Example:

const fetchJoke = async (numberOfPhrases) => {
  const phrasesArray = []
  for (let i = 0; i < numberOfPhrases; i++) {
    const phrase = await fetch(URL_TO_FETCH).then((res) => res.json())
    const fetchedPhrase = await phrase
    phrasesArray.push(fetchedPhrase)
  }
  return phrasesArray
}