Data Structures

• The 2 most basic and used data structures in JavaScript are Objects and Arrays

Arrays

• Arrays are container that are used to store data of a single value
  • Although in JavaScript, Arrays can hold data of any value

Syntax

const commonVariables =[x, y, z]

• Using the new keyword

    const years = new Array (x, y, z)
  

Index of an Array

• arrays are 0-indexed, which means they start from zero

• Elements can be accessed from the array using the

  • Array Name

  • index surrounded by square brackets {}

      const myArray = [100, 200, 300];
      console.log(myArray[0]); // 100
      console.log(myArray[1]); // 200
      console.log(myArray[2]); // 300
    

.length

• we can use the .length property to get the number of elements in an array
  • to get the last element of an array we can write myarray[myarray.length - 1]

.indexOf

• the index of methods tells us the index of the element in the array
• if we try the index of an element that it dosent include we will get -1

.includes

• The modern aproach to check if an element is present in an array
• this method uses stric equality

Array Methods

• Adding Methods

  • .push
    • the push method adds an element as the last element
    • const newLength = friends.push("Bayak, Jhon");
  • .unshift
    • The unshift method adds an array as the first element in the array
      • friends.unshift("Jhon"

• Removing Methods

  • .pop
    • The pop method removes the last element from the array
    • friends.pop()
  • .shift
    • The shift method removes the first element of the array
      • friends.shift()
  • Notice that we do not need to provide any arguments to the pop and shift method

• JavaScript arrays are mutable

  • Even if they are declared using const, the contents can be manipulated by reassigning internal values or using methods like .push() and .pop().

Objects

---

• Objects are basically code used to represent things in your code, these things are defined by a set of characteristics known as properties that consist of keys and value
• the order of the properties doesn't matter

Syntax

const person = {
  name: 'Bayak',
  age: 33,
  likesCoding: true
  };`

• A JavaScript object literal is enclosed with curly braces {}.
• Values are mapped to keys in the object with a colon (:), and
• The key-value pairs are separated by commas.

Retrieve Data

• Bracket notation
  • console.log(jonas[last name])

• Dot notation

  • console.log(jonas.lastname)`

• When to use the Bracket notation and when to use the Dot notation

  • The difference between the dot notation and the bracket notation is we can include expressions inside the bracket like this:
    • const nameKey = 'Name'
    • console.log["last" + namekey]
    • While we can't using the dot notation
  • The dot notation looks cleaner than the bracket notation

• So when to use the dot and the bracket notation?

  • use the dot notation by default, and only use the bracket notation when you need to include an expression

Object Methods

• We can add function expressions as key-value pairs

  • These key-value pairs are known as methods

    calcAge: function(birthyear){
      return 2040 - birthyear
    }
    

• To access methods we can use either the bracket notation or the dot notation

  • jonas.calcAge(1994)

this keyword

• this is a reference to the object

    calcAge: function () {
    return 2040 - this.birthyear
    }