JavaScript Objects

What is an Object? link

An object is a collection of properties, and a property is an association between a name (or key) and a value. A value can be a function, in which case the property is known as a method.

Creating an Object link

There are multiple ways to create objects in JavaScript:

1. Using an object literal:

     let person = {
       firstName: "John",
       lastName: "Doe",
       age: 30,
       fullName: function() {
           return this.firstName + " " + this.lastName;
       }
   };
   
   console.log(person); // {firstName: "John", lastName: "Doe", age: 30, fullName: ƒ}
     

2. Using the Object constructor:

     let person = new Object();
   person.firstName = "John";
   person.lastName = "Doe";
   person.age = 30;
   person.fullName = function() {
       return this.firstName + " " + this.lastName;
   };
   
   console.log(person); // {firstName: "John", lastName: "Doe", age: 30, fullName: ƒ}
     

Accessing Object Properties link

You can access object properties in two ways:

1. Dot notation:

     console.log(person.firstName); // "John"
   console.log(person.age);       // 30
     

2. Bracket notation:

     console.log(person["firstName"]); // "John"
   console.log(person["age"]);       // 30
     

Adding and Modifying Properties link

You can add new properties or modify existing ones using dot or bracket notation:

  person.gender = "male";
person["nationality"] = "American";

person.age = 31;

console.log(person); 
// {firstName: "John", lastName: "Doe", age: 31, fullName: ƒ, gender: "male", nationality: "American"}
  

Removing Properties link

You can remove properties using the delete operator:

  delete person.age;

console.log(person); 
// {firstName: "John", lastName: "Doe", fullName: ƒ, gender: "male", nationality: "American"}
  

Object Methods link

Methods are functions stored as object properties:

  let person = {
    firstName: "John",
    lastName: "Doe",
    fullName: function() {
        return this.firstName + " " + this.lastName;
    }
};

console.log(person.fullName()); // "John Doe"
  

Looping through Object Properties link

You can loop through the properties of an object using a for...in loop:

  for (let key in person) {
    console.log(key + ": " + person[key]);
}
// Output:
// firstName: John
// lastName: Doe
// fullName: function() { return this.firstName + " " + this.lastName; }
  

Nested Objects link

Objects can also contain other objects:

  let person = {
    name: "John",
    age: 30,
    address: {
        street: "123 Main St",
        city: "New York",
        country: "USA"
    }
};

console.log(person.address.city); // "New York"
  

Object.keys(), Object.values(), and Object.entries() link

You can use these methods to get the keys, values, and entries of an object:

  let person = {
    firstName: "John",
    lastName: "Doe",
    age: 30
};

console.log(Object.keys(person));   // ["firstName", "lastName", "age"]
console.log(Object.values(person)); // ["John", "Doe", 30]
console.log(Object.entries(person)); // [["firstName", "John"], ["lastName", "Doe"], ["age", 30]]