TOPIC OVERVIEW

javascript/Objects

Key-value collections with a prototype chain, property descriptors, and more control than they look like they have.

10 QuestionsIntermediateHigh Priority ~12 min read

At their core, JavaScript objects are just collections of key-value pairs, but almost everything in the language — arrays, functions, even class instances — is built on top of this same object model. Every object also has an internal link to a prototype object, and property lookups that don't find a match on the object itself walk up that prototype chain until they find one or hit null — which is how inherited methods work without every object needing its own copy.

Beyond the basic key-value view, every property actually has a descriptor controlling whether it's writable, enumerable, and configurable, which is what Object.freeze, Object.seal, and getters/setters are built on. Understanding property descriptors explains behavior that otherwise looks like magic — why a 'frozen' object's nested objects are still mutable, or why a for...in loop skips some properties that Object.keys shows.

What you'll walk away knowing

How the prototype chain works, and why property lookup misses fall through to it

What property descriptors (writable, enumerable, configurable) control, and how they're set

Why Object.freeze only performs a shallow freeze, and what that means for nested objects

The practical difference between for...in, Object.keys, and Object.getOwnPropertyNames

1What are Objects?Beginner 2What are the properties of an object?Beginner 3How does javascript implements object oriented programming?Intermediate 4What are the key differences between javascript’s Object-based Inheritance and Conventional Class-based Inheritance?Intermediate 5What is a prototype in JavaScript?Intermediate 6How we can implement prototype-based inheritance?Intermediate 7Explain the prototype chain and its role in property lookup.Intermediate 8What is prototype pollution, and how can it be a security risk in JavaScript?Intermediate 9Is modifying or extending built-in object prototypes recommended (e.g., adding a method to `Array.prototype`)? Why or why not?Intermediate 10How does the `Object.prototype.hasOwnProperty()` method work?Intermediate 11How can you optimize prototype chain lookup for better performance?Intermediate 12How can you prevent or mitigate prototype pollution vulnerabilities in your code?Advanced 13What are different methods to create an object?Intermediate 14What do the built in Object constructors do in JavaScript ?Intermediate 15How are constructor functions used to create objects with shared properties and methods?Intermediate 16Can you explain how `Object.prototype.constructor` property works?Intermediate 17How can you add new properties and methods to the prototype of an existing constructor function?Intermediate 18What is the difference between modifying the prototype of an object and adding a property directly to the object?Intermediate 19What does the `Object.create()` method do?Intermediate 20Write a function flattenObject(obj) that flattens a deeply nested object into a single-level object, using dot notation for nested keys.Beginner 21What is an object initializer?Beginner 22Show an example of ES6 classes to create objects and inherit properties?Intermediate 23What is the purpose of the `Object.keys()` method?Beginner 24Explain how the `instanceof` operator works.Intermediate 25What is the difference between an object's `__proto__` and a constructor function's `prototype` property and [[Prototype]]?Intermediate 26What is static dispatching in object-oriented programming?Intermediate 27How does JavaScript handle circular references in object prototypes?Advanced 28What are object wrappers for primitive type?Intermediate 29Can you explain the use of object wrappers with examples?Intermediate 30What happens when you try to access a property that doesn't exist on an object?Beginner 31What is the constructor function?Intermediate 32What are factory functions in JavaScript ?Intermediate

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