Data Structure: Objects in JavaScript

Overview

Objects are unordered key‑value stores. Keys are strings or symbols; values can be any type.

Objects are not iterable by default; use helpers to enumerate properties.

const obj = {
  name: 'Biswas',
  age: 30,
}

console.log(obj);

Result:

{ name: 'Biswas', age: 30 }

console.log(obj.name);
console.log(obj['age']);

Result:

Biswas
30

Add or update properties:

obj.gender = 'Male';

Result:

{ name: 'Biswas', age: 30, gender: 'Male' }

Remove properties:

delete obj.gender;

Result:

{ name: 'Biswas', age: 30 }

const obj = {
  name: 'Biswas',
  age: 30,
  sayName: function() {
    console.log(this.name);
  }
}

Call the method:

obj.sayName();

Result:

Biswas

Examples:

console.log(Object.keys(obj));

Result:

[ 'name', 'age' ]

console.log(Object.values(obj));

Result:

[ 'Biswas', 30 ]

console.log(Object.entries(obj));

Result:

[ [ 'name', 'Biswas' ], [ 'age', 30 ] ]

const city = obj?.address?.city ?? 'Unknown';

const frozen = Object.freeze({ a: 1 });       // shallow freeze
const sealed = Object.seal({ a: 1 });         // can modify, not add/remove

Shallow clone:

const original = { a: 1, nested: { b: 2 } };
const clone1 = { ...original };
const clone2 = Object.assign({}, original);

Deep clone:

const deep = structuredClone(original);

Merge:

const defaults = { retries: 3, verbose: false };
const env = { verbose: true };
const cfg = { ...defaults, ...env };