JavaScript

Last Updated: 12/14/2022

Reference Types

  • In the reference types category, you have objects, arrays, and functions.

Object

  • An object in JavaScript and any other programming languages is like an object in real life. eg car, mobile, person
  • Think of a person. A person has name, age, address and so on. These are the properties of a person.
  • So when you're dealing with multiple related variables, you can put these variables inside of an object.
let name = "ganesh";
let age = "20";
  • Here you have two variables name and age, they're highly related, they are part of the representation of a person, so instead of declaring two variables, you can declare the person object and reference the person object, it makes our code cleaner.

Syntax

  • You create a JavaScript object with an object literal
  • You add one or more key:value pairs inside the object. The keys are the properties of the object.

let person = { name: "ganesh", age: 20 }

Accessing Properties

  • There are two ways to work with these properties: dot notation and bracket notation

Dot notation

  • Shorter

Read property console.log(person.name);

Write property person.name = "kumar"

Bracket notation

  • Useful when the property is available at runtime

Read property console.log(person["name"]);

Write property person["name"] = "kumar"

Arrays

  • Array, is a data structure to represent a list of items.
  • For example, the list of products in a shopping cart, or the list of countries

Creating an Array

  • Square brackets is array literal, and they indicate an empty array. let countries = []; //Array Literal

Initialize an Array

let countries = ["India", "US"];

  • Now we can initialize this array and add a couple of items

Items

  • Each item has an index, and that determines that position of the item in that array.
  • Length of arrays as well as the type of objects you have in an array are dynamic,
  • You can add another item to this array, so the array will expand.
  • Unlike other programming languages, where every item or every object in the array, should have the same type, in JavaScript you can store different types in an array.
  • Technically an array is an object, it has a bunch of key value pairs, or properties that you can access using the dot notation
  • Length property returns a number of items or elements in an array

Functions

  • A JavaScript function is a set of statements that either performs a task or calculates and returns a value.

Syntax

function name() {
  // code to be executed
}
function name(parameter1, parameter2, parameter3) {
  // code to be executed
}

Declaring Function

function greet() {
	console.log("Hello World");
}

Invoking/Calling Function

greet();

Parameters

  • Functions can have inputs/parameters, and these inputs can change how the function behaves.
  • Parameter is like a variable that is accessible inside of the function and is not accessible outside of the function
  • Argument is the actual value you supply for the parameter.
  • You can reuse function but with a different input.
  • Function can have multiple parameters. Separate parameters using a comma

Type of Functions

  • Performing a task
  • Calculate something

A real world application is essentially a collection of hundreds or thousands of functions working together to provide the functionality of that application.

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