What is an Object in JavaScript?

In JavaScript, an object is one of the fundamental data structures that allows storing values in key:value format.

Let's say you want to describe a person's data: the best option for this is an object.

    const person = {
      firstName: "Aram",
      lastName: "Khachatryan",
      age: 30,
      isDeveloper: true
    };

This code creates an object named person that stores information about a person.

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How to Access Object Properties

There are two ways:

1. Dot Notation

    console.log(person.firstName); // Aram

2. Bracket Notation

    console.log(person["lastName"]); // Khachatryan

Bracket notation is useful when the property name is stored in a variable:

    const key = "age";
    console.log(person[key]); // 30

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How to Modify and Add Properties

    person.age = 31; // modifies existing value
    person.city = "Yerevan"; // adds new property

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Object Methods

We can also add functions to objects, which we call methods.

    const person = {
      firstName: "Aram",
      lastName: "Khachatryan",
      fullName() {
        return this.firstName + " " + this.lastName;
      }
    };
    
    console.log(person.fullName()); // Aram Khachatryan

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Useful Object Methods

• Object.keys(obj) - returns an array of all keys
• Object.values(obj) - returns an array of all values
• Object.entries(obj) - returns an array of key-value pairs

    const keys = Object.keys(person);      // ['firstName', 'lastName']
    const values = Object.values(person);  // ['Aram', 'Khachatryan']
    const entries = Object.entries(person);
    // [['firstName', 'Aram'], ['lastName', 'Khachatryan']]

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Object Comparison (===)

    const a = { x: 1 };
    const b = { x: 1 };
    
    console.log(a === b); // false

Objects are compared by reference, not by content.

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Object Cloning

In JavaScript, when you simply assign an object from one variable to another, you're actually copying the reference, not the object itself.

    const original = { name: "Aram" };
    const copy = original;
    
    copy.name = "Mariam";
    
    console.log(original.name); // Mariam

This way, both variables reference the same object.

Proper Cloning with Object.assign

    const original = { name: "Aram" };
    const copy = Object.assign({}, original);
    
    copy.name = "Mariam";
    
    console.log(original.name); // Aram

Or using Spread Operator

    const copy = { ...original };

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Nested Objects

When an object contains another object:

    const user = {
      name: "Aram",
      contact: {
        email: "aram@example.com",
        phone: "099123456"
      }
    };

Accessing:

    console.log(user.contact.email); // aram@example.com

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Cloning Limitations

Object.assign or { ...obj } don't perform deep cloning of nested objects.

    const clone = { ...user };
    clone.contact.email = "mariam@example.com";
    
    console.log(user.contact.email); // mariam@example.com

Here, while the top level is cloned, contact still references the same object.

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Solution: Deep Clone

Simplest method: JSON hack (works only if object doesn't contain functions)

    const deepClone = JSON.parse(JSON.stringify(user));

Or use libraries like lodash's cloneDeep.

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Object.assign vs Spread Operator

Feature	Object.assign	Spread Operator
Syntax	Long	Short
Deep Clone	❌	❌
Merge Multiple	✅	✅

    const a = { x: 1 };
    const b = { y: 2 };
    const merged1 = Object.assign({}, a, b);
    const merged2 = { ...a, ...b };