Objects in JavaScript

has key-value pairs, separated by colon. The key is also known as property
Similarity: index of arrays are replaced by keys in objects.
Object literal syntax is directly writing properties inside {}
Order during retrieval does not matter in case of objects whereas order matters in arrays.

Arrays: used for structured data
Objects: used for unstructured data

Property lookup methods in objects:

1. using dot notation
2. using brackets notation: key is defined as string in [] inside quotes, the key name can be an expression also. Ex. obj['firstName']; Ex. obj[2+3]; Putting an expression won't work with dot notation. We need to use the final property name, and not the computed property name.

Hence, when we have a computed property name its recommended to use brackets notation.

undefined will be returned if a property doesn't exist and we try to access it.

obj['insta-id'] = '@juju';

Refer operator precedence table on MDN for more info.

Object Methods

Fns are a type of value. Hence, we can create key-value pair in which the value is a fn. Means, we can add fns to objects.
Fn expression becomes methods inside objects i.e a fn attached to an object as a value for a key.
Fn declaration inside an object won't work.
method is also a property on the object which holds a fn value.
We can have values in the form of : array, string, boolean, fn etc.
obj.propName(); // will get the fn value and execute it using the ()

'this' : refers to the object on which its called

const person = {
  fName: 'Raja',
  lName: 'Rajeshwar',
  bYear: 1970,
  job: 'King',
  friends: ["Billu","Penchu","Ramesh"],

  calcAge: function(){
    // this will be the object which has called this method.
    // Its used to reference the object, and not hardcode it.
    console.log(this);
    // a new property is created on the person object named 'age'
    this.age = 2024 - this.bYear
    return this.age;
  }
}

person.calcAge(1970);
// age property will only exist if this fn was called atleast once else it won't exist.
person.age;

Arrays, Fns are all under the hood objects in JS. Hence, they have their own methods.