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JavaScript

Interview questions & answers

Browser & Node — types, async, DOM, ES6+.

102 questions

Question 1
What is JavaScript?
A high-level, dynamic language standardized as ECMAScript. It runs in browsers (with the DOM and Web APIs) and on servers with runtimes like Node.js.
Example code
```
console.log(typeof window !== "undefined" ? "browser" : "node");
```
Question 2
What is the difference between let, const, and var?
var is function-scoped and hoisted with an initial undefined; let and const are block-scoped, live in the temporal dead zone until declared, and const cannot be rebound (object contents may still change).
Example code
```
let x = 1;
const y = 2;
var z = 3;
console.log(x + y + z);
```
Question 3
What is hoisting?
Declarations are registered in scope before execution: var becomes undefined until assigned; function declarations are fully initialized early; let/const/class throw if accessed before their line.
Example code
```
console.log(typeof hoist);
var hoist = 1;
function hoistFn() {}
```
Question 4
What is a closure?
A function that remembers variables from an enclosing lexical scope after the outer function returns. Used for modules, callbacks, and factories.
Example code
```
function outer() {
  let n = 0;
  return () => ++n;
}
const c = outer();
console.log(c(), c());
```
Question 5
How is this determined in JavaScript?
For normal functions: set by call site (new, method call, call/apply/bind, or global/undefined in a bare call in sloppy/strict mode). Arrow functions inherit this lexically.
Example code
```
const o = {
  name: "a",
  fn() { return this.name; },
};
console.log(o.fn());
```
Question 6
What is the difference between == and ===?
=== compares without coercion (type and value). == allows coercion and is easy to misuse; prefer === in almost all code.
Example code
```
console.log(0 == false, 0 === false);
```
Question 7
Why does typeof null return "object"?
A historical implementation artifact kept for backward compatibility. Use value === null to test for null.
Example code
```
console.log(typeof null, null === null);
```
Question 8
What are primitive vs reference types?
Primitives (string, number, boolean, bigint, symbol, undefined, null) are copied by value. Objects, arrays, and functions are references; assignment shares the same identity.
Example code
```
let o = { x: 1 };
let o2 = o;
o2.x = 2;
console.log(o.x);
```
Question 9
What is NaN?
Not-a-Number is a numeric value from invalid math. NaN !== NaN; use Number.isNaN for checks.
Example code
```
console.log(Number.isNaN(NaN), NaN === NaN);
```
Question 10
What is the prototype chain?
Property lookup walks from the object to Object.prototype (and beyond) via [[Prototype]] until a property is found or the chain ends.
Example code
```
const p = { a: 1 };
console.log(Object.getPrototypeOf(p) === Object.prototype);
```
Question 11
What does the class keyword do?
Syntactic sugar over prototype inheritance: methods on the prototype, static methods on the constructor, extends wires the prototype chain.
Example code
```
class A { m() { return 1; } }
console.log(new A().m());
```
Question 12
What does new do?
Creates an object linked to Constructor.prototype, runs the constructor with that this, and returns the object unless an object is explicitly returned.
Example code
```
function Box(v) { this.v = v; }
console.log(new Box(3).v);
```
Question 13
What is the event loop?
Runs JS on one thread: execute the stack, then process microtasks, then macrotasks (timers, I/O), keeping the UI responsive when work is async.
Example code
```
setTimeout(() => console.log("macrotask"), 0);
Promise.resolve().then(() => console.log("microtask"));
```
Question 14
Microtasks vs macrotasks?
Microtasks (Promise.then, queueMicrotask) run before the next macrotask and can run to completion in a burst. Macrotasks include setTimeout and many I/O callbacks.
Example code
```
Promise.resolve().then(() => console.log("runs before next macrotask"));
```
Question 15
What are Promise states?
Pending, then fulfilled with a value or rejected with a reason. Once settled, state does not change; then/catch return new Promises for chaining.
Example code
```
Promise.resolve(1).then((x) => x + 1).then(console.log);
```
Question 16
What is async/await?
async functions return Promises; await pauses the function until a Promise settles, with errors propagating as rejections unless caught with try/catch.
Example code
```
async function f() {
  return await Promise.resolve(2);
}
f().then(console.log);
```
Question 17
What is strict mode?
'use strict' enables stricter parsing and runtime checks: fewer silent errors, no accidental globals in assignments, and more predictable this in functions.
Example code
```
"use strict";
function g() { return (function () { return this; })(); }
console.log(g());
```
Question 18
What is the temporal dead zone?
The span from block entry until let/const/class is initialized; reading those bindings throws ReferenceError.
Example code
```
// let x; before use → ReferenceError (TDZ)
function t() { console.log(typeof undeclared); }
```
Question 19
What are call, apply, and bind?
call/apply invoke a function with an explicit this and arguments (spread vs array). bind returns a new function with a fixed this and optional partial arguments.
Example code
```
function add(a, b) { return a + b; }
console.log(add.call(null, 1, 2), add.apply(null, [1, 2]));
```
Question 20
Debounce vs throttle?
Debounce runs after input quiets (search boxes). Throttle runs at most once per interval (scroll handlers). Both limit expensive work.
Example code
```
function debounce(fn, ms) {
  let t;
  return (...a) => {
    clearTimeout(t);
    t = setTimeout(() => fn(...a), ms);
  };
}
```
Question 21
What is event delegation?
Attach one listener on a parent and handle events from children via event.target, reducing listeners and handling dynamic content.
Example code
```
// ul.addEventListener("click", (e) => { if (e.target.matches("li")) { ... } });
```
Question 22
Event bubbling vs capturing?
Events travel capture phase (root to target) then bubble (target to root). stopPropagation and defaultPrevented control flow.
Example code
```
// el.addEventListener("click", handler, { capture: true });
```
Question 23
Shallow vs deep copy?
Shallow copy duplicates top-level fields; nested objects stay shared. Deep copy duplicates nested graphs (structuredClone, libraries, or careful recursion).
Example code
```
const a = { x: { y: 1 } };
const b = { ...a };
b.x.y = 9;
console.log(a.x.y);
```
Question 24
map vs forEach?
map returns a new array of transformed values; forEach returns undefined and is for side effects. map is composable; forEach cannot be chained for results.
Example code
```
console.log([1, 2, 3].map((n) => n * 2));
```
Question 25
What is a pure function?
Same inputs always yield the same output and there are no observable side effects; easier to test and reason about.
Example code
```
const sum = (a, b) => a + b;
console.log(sum(1, 2));
```
Question 26
What is a higher-order function?
A function that takes functions as arguments or returns a function (e.g. map, filter, reduce, middleware patterns).
Example code
```
const twice = (f) => (x) => f(f(x));
console.log(twice((x) => x + 1)(0));
```
Question 27
What are ES modules?
import/export static structure enables tree shaking and async loading; distinct from CommonJS require in semantics and loading rules.
Example code
```
// export const x = 1;  // in module
// import { x } from "./mod.js";
```
Question 28
What is tree shaking?
Bundlers eliminate unused exports when the module graph is statically analyzable, shrinking production bundles.
Example code
```
// unused exports can be dropped when bundler tree-shakes
```
Question 29
typeof vs instanceof?
typeof returns a string type tag for primitives and 'function'/'object'. instanceof tests prototype chain membership for objects.
Example code
```
console.log(typeof 1, [] instanceof Array);
```
Question 30
What is JSON?
A text format for data interchange, a subset of JS literal syntax. JSON.parse/stringify bridge objects and strings; not all JS values round-trip.
Example code
```
const o = { a: 1 };
console.log(JSON.stringify(o));
```
Question 31
What is CORS?
Browser security policy: cross-origin HTTP requests need server headers allowing the origin (or credentials rules). Same-origin policy blocks reads without permission.
Example code
```
// fetch("/api").then((r) => r.json())
```
Question 32
XSS in one sentence?
Untrusted input rendered as HTML/JS can execute script in a victim's browser; mitigate with escaping, CSP, and safe APIs.
Example code
```
const esc = (s) => s.replace(/</g, "&lt;");
console.log(esc("<b>"));
```
Question 33
What is a Web Worker?
A separate thread with message passing; no DOM access. Offloads CPU work from the main thread to keep the UI smooth.
Example code
```
// const w = new Worker("worker.js");
// w.postMessage("ping");
```
Question 34
What is the difference between SPA and MPA?
SPA updates in-page via JS routing and APIs; MPA loads full new documents from the server. Tradeoffs: SEO, complexity, and perceived performance.
Example code
```
// history.pushState({}, "", "/app/route");
```
Question 35
npm lockfile purpose?
Pins transitive dependency versions for reproducible installs across machines and CI (package-lock.json).
Example code
```
// package-lock.json pins dependency tree
```
Question 36
What does a bundler do?
Resolves modules, may transpile, tree-shake, and emit optimized assets for browsers (e.g. Vite, webpack, Rollup).
Example code
```
// vite build / webpack for production bundles
```
Question 37
What is Babel?
A toolchain that transpiles modern JS (and JSX/TS) to older syntax so it runs on older engines per your targets.
Example code
```
// babel transforms modern syntax for older engines
```
Question 38
What is hydration?
In SSR frameworks, attaching client-side listeners and state to server-rendered HTML so the page becomes interactive.
Example code
```
// hydrate client React/Vue on SSR HTML
```
Question 39
What is Symbol in JavaScript?
Unique, non-string property keys; often used for internal metadata that won't collide with string keys.
Example code
```
const k = Symbol("id");
const user = { [k]: 42, name: "Ann" };
console.log(user[k]);
```
Question 40
What is Iterator in JavaScript?
Objects with next() following the iterator protocol; consumed by for...of and spread when iterable.
Example code
```
const it = [1, 2][Symbol.iterator]();
console.log(it.next(), it.next());
```
Question 41
What is Generator in JavaScript?
function* yields values lazily; iterators pause/resume execution and can yield to other generators.
Example code
```
function* gen() {
  yield 1;
  yield 2;
}
console.log([...gen()]);
```
Question 42
What is Proxy in JavaScript?
Intercepts operations on an object (get, set, etc.) for logging, validation, or reactive patterns.
Example code
```
const t = new Proxy({}, { get: () => 1 });
console.log(t.any);
```
Question 43
What is Reflect in JavaScript?
A built-in object with methods mirroring internal operations, often used with Proxy for default behavior.
Example code
```
const o = {};
Reflect.set(o, "x", 1);
console.log(o.x);
```
Question 44
What is WeakMap in JavaScript?
Keys are objects only; entries can be GC'd when keys are unreachable—useful for private-ish associations without leaks.
Example code
```
const wm = new WeakMap();
wm.set({}, 1);
```
Question 45
What is WeakSet in JavaScript?
Like WeakMap but only stores objects in a set; weakly held for caches or tagging without retaining objects.
Example code
```
const ws = new WeakSet();
ws.add({});
```
Question 46
What is BigInt in JavaScript?
Arbitrary-precision integers; cannot mix with Number in arithmetic without explicit conversion.
Example code
```
const n = 10n ** 20n;
console.log(n.toString());
```
Question 47
What is Optional chaining in JavaScript?
obj?.prop short-circuits on null/undefined instead of throwing; pairs with ?? for defaults.
Example code
```
const o = { a: null };
console.log(o.a?.b?.c);
```
Question 48
What is Nullish coalescing in JavaScript?
a ?? b returns b only when a is null or undefined, unlike || which treats many values as falsy.
Example code
```
console.log(0 ?? 1, null ?? 1);
```
Question 49
What is Template literals in JavaScript?
Backtick strings with ${} interpolation and multiline text; tagged templates pass segments to a function.
Example code
```
const n = 3;
console.log(`two plus one is ${n}`);
```
Question 50
What is Destructuring in JavaScript?
Unpack object properties or array elements into variables, including defaults and rest patterns.
Example code
```
const { a, b = 1 } = { a: 0 };
const [x, y] = [1, 2];
console.log(a, b, x, y);
```
Question 51
What is Spread operator in JavaScript?
Expands iterables in arrays, calls, or object literals (own enumerable properties for objects).
Example code
```
console.log([1, ...[2, 3]]);
console.log({ ...{ a: 1 }, b: 2 });
```
Question 52
What is Rest parameters in JavaScript?
Collect remaining arguments into an array: function f(a, ...rest) { }
Example code
```
function f(a, ...r) { return r.length; }
console.log(f(1, 2, 3));
```
Question 53
What is Object.freeze in JavaScript?
Makes an object shallowly immutable: cannot add/change/remove own properties (nested objects unaffected unless frozen too).
Example code
```
const o = Object.freeze({ x: 1 });
// o.x = 2; // silent fail in non-strict
```
Question 54
What is Object.assign in JavaScript?
Copies enumerable own properties from sources to a target; shallow merge pattern for options objects.
Example code
```
console.log(Object.assign({ a: 1 }, { b: 2 }));
```
Question 55
What is Array.prototype.flat in JavaScript?
Flattens nested arrays to a depth; flatMap maps then flattens one level—handy for nested lists.
Example code
```
console.log([[1], [2, [3]]].flat(2));
```
Question 56
What is Array.prototype.sort in JavaScript?
Sorts in place; comparator (a,b) => a-b for numbers. Engine stability and coercion rules matter in interviews.
Example code
```
const a = [10, 2, 1];
a.sort((x, y) => x - y);
console.log(a);
```
Question 57
What is Set in JavaScript?
Collection of unique values; fast membership checks; iteration order follows insertion for modern engines.
Example code
```
const s = new Set([1, 1, 2]);
console.log(s.size);
```
Question 58
What is Map in JavaScript?
Key/value with arbitrary keys (including objects); preserves insertion order; distinct from plain objects for frequent adds/removes.
Example code
```
const m = new Map([["a", 1]]);
console.log(m.get("a"));
```
Question 59
What is Promise.all in JavaScript?
Fulfills with an array of results when all inputs fulfill; rejects on first rejection.
Example code
```
Promise.all([1, 2].map((x) => Promise.resolve(x))).then(console.log);
```
Question 60
What is Promise.allSettled in JavaScript?
Waits for all to settle; never rejects the aggregate—useful when partial failure is OK.
Example code
```
Promise.allSettled([Promise.resolve(1), Promise.reject(2)]).then(console.log);
```
Question 61
What is Promise.race in JavaScript?
Settles with the first settled input promise—timeouts and racing requests.
Example code
```
Promise.race([new Promise((r) => setTimeout(() => r(1), 50)), Promise.resolve(2)]).then(console.log);
```
Question 62
What is queueMicrotask in JavaScript?
Schedules a microtask; runs before the next macrotask—use sparingly to avoid starvation.
Example code
```
queueMicrotask(() => console.log("micro"));
```
Question 63
What is requestAnimationFrame in JavaScript?
Schedules work before the next repaint; ideal for smooth animations vs setInterval.
Example code
```
requestAnimationFrame(() => console.log("frame"));
```
Question 64
What is MutationObserver in JavaScript?
Watches DOM changes asynchronously; used when integrating with dynamic third-party markup.
Example code
```
// new MutationObserver(cb).observe(el, { childList: true });
```
Question 65
What is Intersection Observer in JavaScript?
Efficiently detects element visibility in the viewport; lazy-loading images and infinite scroll.
Example code
```
// new IntersectionObserver(cb).observe(img);
```
Question 66
What is CustomEvent in JavaScript?
Dispatch structured events on DOM or EventTarget with detail payloads for decoupled components.
Example code
```
const e = new CustomEvent("x", { detail: { id: 1 } });
dispatchEvent(e);
```
Question 67
What is History API in JavaScript?
pushState/replaceState enable client-side routing without full reloads; popstate handles back/forward.
Example code
```
history.pushState({ id: 1 }, "", "/x");
window.addEventListener("popstate", () => {});
```
Question 68
What is Service Worker in JavaScript?
Proxy for network/cache offline-first PWA patterns; separate from the page and event-driven.
Example code
```
// navigator.serviceWorker.register("/sw.js");
```
Question 69
What is WebSocket in JavaScript?
Full-duplex persistent connection after HTTP upgrade; low-latency chat and live feeds.
Example code
```
// const ws = new WebSocket("wss://host");
// ws.onmessage = (e) => console.log(e.data);
```
Question 70
What is fetch API in JavaScript?
Promise-based HTTP; remember to check response.ok and handle JSON/text streams explicitly.
Example code
```
fetch("/api")
  .then((r) => {
    if (!r.ok) throw new Error(String(r.status));
    return r.json();
  })
  .catch(console.error);
```
Question 71
What is AbortController in JavaScript?
Signals cancellation to fetch and other async APIs; abort() rejects with AbortError.
Example code
```
const c = new AbortController();
fetch("/slow", { signal: c.signal });
c.abort();
```
Question 72
What is Content Security Policy in JavaScript?
HTTP header restricting script/style sources to mitigate XSS; report-only mode helps rollout.
Example code
```
// Content-Security-Policy: default-src 'self'
```
Question 73
What is SameSite in JavaScript?
Cookie attribute reducing CSRF risk: Strict/Lax/None with Secure for cross-site contexts.
Example code
```
// Set-Cookie: sid=...; SameSite=Lax; Secure
```
Question 74
What is localStorage in JavaScript?
Origin-scoped key/value storage synchronous API; persists until cleared; size limits apply.
Example code
```
localStorage.setItem("k", "v");
console.log(localStorage.getItem("k"));
```
Question 75
What is sessionStorage in JavaScript?
Like localStorage but scoped to the tab/session lifetime.
Example code
```
sessionStorage.setItem("t", "1");
```
Question 76
What is IndexedDB in JavaScript?
Async structured client database for larger offline datasets; more complex than Storage API.
Example code
```
// indexedDB.open("db", 1)
```
Question 77
What is import in JavaScript?
Dynamic import() returns a Promise of a module; enables code splitting and conditional loading.
Example code
```
const mod = await import("./other.js");
```
Question 78
What is Top-level await in JavaScript?
Allowed in ES modules to await at module load; blocks graph evaluation for that module.
Example code
```
// await fetch("/x") // only valid in ES modules
```
Question 79
What is package.json exports in JavaScript?
Conditional entry points and subpath exports control what consumers can import from a package.
Example code
```
// "exports": { ".": "./index.js" }
```
Question 80
What is CommonJS interop in JavaScript?
Default interop between require and ESM differs by bundler/runtime; __esModule and default export nuances appear in tooling questions.
Example code
```
// const x = require("esm-pkg");
```
Question 81
What is Intl in JavaScript?
Internationalization API for collation, number/date formatting, and locale-aware UI without heavy libraries.
Example code
```
console.log(new Intl.NumberFormat("en-IN").format(1234567));
```
Question 82
What is Structured clone in JavaScript?
structuredClone deep-clones many types (including Map/Set) better than JSON for structured data.
Example code
```
const c = structuredClone(new Map([["a", 1]]));
console.log(c.get("a"));
```
Question 83
What is WeakRef in JavaScript?
Holds a weak reference to an object; FinalizationRegistry runs callbacks after GC—advanced memory patterns.
Example code
```
let o = { x: 1 };
const r = new WeakRef(o);
o = null;
```
Question 84
What is Atomics in JavaScript?
Low-level atomic operations on SharedArrayBuffer for synchronization between workers (niche but asked in specialized roles).
Example code
```
// SharedArrayBuffer + Atomics.add(...)
```
Question 85
What is Error causes in JavaScript?
Error.cause chains underlying errors for clearer async stack traces in modern engines.
Example code
```
throw new Error("outer", { cause: new Error("inner") });
```
Question 86
What is Private class fields in JavaScript?
#field true privacy in classes (not just convention); not visible on the instance object enumeration.
Example code
```
class C {
  #x = 1;
  get x() { return this.#x; }
}
console.log(new C().x);
```
Question 87
What is Static class blocks in JavaScript?
Static {} runs once per class evaluation for setup side effects adjacent to class syntax.
Example code
```
class C {
  static x;
  static { this.x = 1; }
}
```
Question 88
What is Temporal (proposal/status) in JavaScript?
Modern date/time API aiming to replace Date pitfalls; know that Date remains dominant in production today.
Example code
```
// Temporal API — check browser/runtime support
```
Question 89
What is SIMD in JavaScript?
Single-instruction multiple-data for numeric vectors—browser support limited; more common in native/HPC contexts.
Example code
```
// SIMD.js limited; often use WebAssembly for vectors
```
Question 90
What is Realms (advanced) in JavaScript?
Isolated global environments; relevant to secure sandboxing and iframe/worker boundaries in advanced security questions.
Example code
```
// iframe.contentWindow separate realm
```
Question 91
What is IIFE in JavaScript?
Immediately invoked function expression creates a scope; legacy pattern before modules.
Example code
```
(function () {
  const secret = 1;
  console.log(secret);
})();
```
Question 92
What is Memoization in JavaScript?
Caching results of expensive pure calls; watch memory and cache invalidation.
Example code
```
function memo(fn) {
  const c = new Map();
  return (k) => (c.has(k) ? c.get(k) : c.set(k, fn(k)).get(k));
}
```
Question 93
What is SSR in JavaScript?
Server renders HTML first for faster first paint and SEO; client hydrates.
Example code
```
// res.send(renderToString(<App />));
```
Question 94
What is CSR in JavaScript?
Client fetches data and renders; simpler hosting, worse first-load SEO without mitigation.
Example code
```
// client-only: root.render(<App />);
```
Question 95
What is JWT in JavaScript?
Self-contained signed tokens for stateless auth; validate signature and expiry; mind XSS storage issues.
Example code
```
// header.payload.signature — verify on server only
```
Question 96
What is REST vs GraphQL in JavaScript?
REST uses multiple resource URLs; GraphQL one endpoint with client-shaped queries—tradeoffs in caching and complexity.
Example code
```
// GET /users/1  vs  POST /graphql { user(id:1){name} }
```
Question 97
What is WebAssembly in JavaScript?
Binary instruction format near-native speed in the browser alongside JS; no DOM access from Wasm directly.
Example code
```
// WebAssembly.instantiate(bytes).then(...)
```
Question 98
What is DOMContentLoaded in JavaScript?
Fires when HTML is parsed; defer long tasks to not block parsing.
Example code
```
document.addEventListener("DOMContentLoaded", () => console.log("ready"));
```
Question 99
What is Passive listeners in JavaScript?
{ passive: true } tells the browser scrolling won't be prevented—improves scroll performance.
Example code
```
// addEventListener("touchstart", fn, { passive: true });
```
Question 100
What is Lazy loading images in JavaScript?
loading="lazy" defers offscreen images; improves LCP and bandwidth.
Example code
```
// <img src="x.jpg" loading="lazy" alt="" />
```
Question 101
What is Semantic HTML in JavaScript?
Correct elements (nav, main, article) improve accessibility, SEO, and maintainability.
Example code
```
// <main><article><nav> instead of only <div>
```
Question 102
What is ARIA in JavaScript?
Attributes augment accessibility when native semantics aren't enough; prefer native elements first.
Example code
```
// <button aria-expanded="false">Menu</button>
```

What is JavaScript?

What is the difference between let, const, and var?

What is hoisting?

What is a closure?

How is this determined in JavaScript?

What is the difference between == and ===?

Why does typeof null return "object"?

What are primitive vs reference types?

What is NaN?

What is the prototype chain?

What does the class keyword do?

What does new do?

What is the event loop?

Microtasks vs macrotasks?

What are Promise states?

What is async/await?

What is strict mode?

What is the temporal dead zone?

What are call, apply, and bind?

Debounce vs throttle?

What is event delegation?

Event bubbling vs capturing?

Shallow vs deep copy?

map vs forEach?

What is a pure function?

What is a higher-order function?

What are ES modules?

What is tree shaking?

typeof vs instanceof?

What is JSON?

What is CORS?

XSS in one sentence?

What is a Web Worker?

What is the difference between SPA and MPA?

npm lockfile purpose?

What does a bundler do?

What is Babel?

What is hydration?

What is Symbol in JavaScript?

What is Iterator in JavaScript?

What is Generator in JavaScript?

What is Proxy in JavaScript?

What is Reflect in JavaScript?

What is WeakMap in JavaScript?

What is WeakSet in JavaScript?

What is BigInt in JavaScript?

What is Optional chaining in JavaScript?

What is Nullish coalescing in JavaScript?

What is Template literals in JavaScript?

What is Destructuring in JavaScript?

What is Spread operator in JavaScript?

What is Rest parameters in JavaScript?

What is Object.freeze in JavaScript?

What is Object.assign in JavaScript?

What is Array.prototype.flat in JavaScript?

What is Array.prototype.sort in JavaScript?

What is Set in JavaScript?

What is Map in JavaScript?

What is Promise.all in JavaScript?

What is Promise.allSettled in JavaScript?

What is Promise.race in JavaScript?

What is queueMicrotask in JavaScript?

What is requestAnimationFrame in JavaScript?

What is MutationObserver in JavaScript?

What is Intersection Observer in JavaScript?

What is CustomEvent in JavaScript?

What is History API in JavaScript?

What is Service Worker in JavaScript?

What is WebSocket in JavaScript?

What is fetch API in JavaScript?

What is AbortController in JavaScript?

What is Content Security Policy in JavaScript?

What is SameSite in JavaScript?

What is localStorage in JavaScript?

What is sessionStorage in JavaScript?

What is IndexedDB in JavaScript?

What is import in JavaScript?

What is Top-level await in JavaScript?

What is package.json exports in JavaScript?

What is CommonJS interop in JavaScript?