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JavaScript

JavaScript language, browser, and Node.js interview recall cards.

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JavaScript cards

43 cards

JavaScript Medium Theory

API and network basics in JavaScript: fetch, XMLHttpRequest, HTTP methods, JSON responses, and error handling in API calls

Frontend and Node.js code often call APIs using `fetch` today, but interviews still expect you to know HTTP basics and sometimes older XHR patterns.

Know common HTTP methods
`fetch` returns a promise
HTTP errors and network failures are not the same thing

#api #javascript #network

API and network basics in JavaScript: fetch, XMLHttpRequest, HTTP methods, JSON responses, and error handling in API calls

JavaScript Medium Theory

Arithmetic, comparison, logical, ternary, nullish coalescing, optional chaining, and short-circuit operators

JavaScript operators cover math, comparisons, boolean logic, fallback values, safe property access, and concise branching.

`??` differs from `||`
Optional chaining stops on nullish access
Short-circuiting affects evaluation

#expressions #javascript #operators

Arithmetic, comparison, logical, ternary, nullish coalescing, optional chaining, and short-circuit operators

JavaScript Hard Theory

Asynchronous JavaScript: callbacks, callback hell, promises, promise states, promise chaining, async/await, try/catch with async, Promise.all, Promise.allSettled, Promise.race, and Promise.any

Modern async JavaScript is built on promises and `async`/`await`, but you still need to understand callbacks and promise coordination helpers.

Promises are pending, fulfilled, or rejected
`async` functions return promises
Promise combinators solve different coordination problems

#async #javascript #promises

Asynchronous JavaScript: callbacks, callback hell, promises, promise states, promise chaining, async/await, try/catch with async, Promise.all, Promise.allSettled, Promise.race, and Promise.any

JavaScript Easy Theory

Browser storage in JavaScript: localStorage, sessionStorage, and cookies

Browsers offer several storage mechanisms with different persistence, size, and request-behavior trade-offs.

`localStorage` persists across sessions
`sessionStorage` lasts for the tab session
Cookies can be sent with HTTP requests

#browser #javascript #storage

Browser storage in JavaScript: localStorage, sessionStorage, and cookies

JavaScript Medium Theory

Class syntax, constructor, instance methods, static methods, inheritance, super, encapsulation basics, and polymorphism basics in JavaScript

JavaScript classes provide cleaner syntax over prototype-based behavior, including constructors, instance methods, inheritance, and static members.

`class` is syntax over prototypes
`super` reaches parent behavior
Encapsulation and polymorphism are design ideas, not just keywords

#classes #javascript #oop

Class syntax, constructor, instance methods, static methods, inheritance, super, encapsulation basics, and polymorphism basics in JavaScript

JavaScript Medium Theory

Closures, lexical scope, and practical uses of closures in JavaScript

A closure happens when an inner function keeps access to variables from its lexical outer scope even after the outer function returns.

Scope is determined lexically
Closures retain access to outer variables
Useful for encapsulation and factories

#closures #javascript #scope

Closures, lexical scope, and practical uses of closures in JavaScript

JavaScript Medium Theory

Collections in JavaScript: Set, Map, WeakSet, and WeakMap

JavaScript has keyed and set-like collections beyond plain objects and arrays, including weak collections for object-keyed references.

Map preserves insertion order and allows any key type
Set stores unique values
Weak collections hold weak references to objects only

#collections #data-structures #javascript

Collections in JavaScript: Set, Map, WeakSet, and WeakMap

JavaScript Medium Theory

Common JavaScript comparison topics for interviews

JavaScript interviews often use comparison questions to test whether you understand trade-offs, not just syntax.

Comparisons reveal semantics and trade-offs
Many pairs differ by mutation, coercion, or context
Strong answers use short examples

#comparisons #interview #javascript

Common JavaScript comparison topics for interviews

JavaScript Medium Theory

Constructor functions, prototypes, and the prototype chain in JavaScript

Before class syntax, constructor functions and prototypes were the main way to share behavior, and that model still exists underneath modern classes.

Functions can act as constructors
Shared methods usually live on the prototype
Property lookup follows the prototype chain

#javascript #oop #prototypes

Constructor functions, prototypes, and the prototype chain in JavaScript

JavaScript Easy Theory

Date and time basics in JavaScript: Date object and common date methods

JavaScript's `Date` object represents points in time and exposes local or UTC getters, setters, and formatting helpers.

Dates are stored as timestamps
Timezone handling can surprise people
Common methods expose year, month, day, and time parts

#basics #date #javascript

Date and time basics in JavaScript: Date object and common date methods