Frontend Interview Questions Bank | Coding, System Design, Concepts

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139 matches

Coding

Debounce Function

Implement debounce(fn, wait) that delays execution until the user stops triggering events. Clear the previous timer on e…

IntermediateHighJavaScript

Coding

Box Model: Margin, Padding, Border

Build a card layout that clearly demonstrates the CSS box model. Use padding to add internal breathing room, a border to…

EasyHighCSS

Coding

Semantic Page Layout

Build a semantic page layout using header, nav, main, section, article, and footer. Focus on correct landmarks, heading…

EasyHighHTML

Coding

Flexbox: Responsive Navbar

Build a responsive navbar using Flexbox. Align brand left, links center or right, and actions to the end. Use gap for sp…

IntermediateHighCSS

Coding

Forms & Pseudo-classes: Focus, Invalid, Required, Helper Text

Style form fields using :focus, :invalid, and :required to guide users. Show clear focus rings, error borders, and helpe…

IntermediateHighCSS

Coding

Grid: Card Gallery (2→4 Columns)

Create a responsive card gallery using CSS Grid that adapts from 2 to 4 columns. Use `repeat()` with `minmax()` for flex…

IntermediateHighCSS

Coding

Tables and Accessibility

The goal is to provide a semantic table that screen readers can navigate, with a clear caption and correct header associ…

IntermediateHighHTML

Coding

Theming with CSS Variables: OS Dark Mode + Manual Override

Create a themeable panel using ONLY CSS custom properties. Define light defaults on :root, redefine the SAME variables f…

IntermediateHighCSS

Coding

Contact Form with Proper Labels

The success message should only appear after a valid submit, so native validation must be enabled and the form action sh…

EasyHighHTML

Coding

Links and Images

Create semantic links and images: use anchor elements with descriptive text, add target/rel when opening new tabs, and i…

EasyHighHTML

Coding

Positioning: Relative/Absolute Badge

This pattern is used in notifications, status indicators, and card metadata, so the badge should remain anchored even as…

EasyHighCSS

Coding

SEO: Essential <head> Metadata

You’re given a simple marketing page that renders fine in the browser, but it’s missing production-grade <head> metadata…

EasyHighHTML

Coding

Shallow Clone (Object or Array)

Create a shallow copy of an array or object. Copy top-level properties but keep nested references intact, and document t…

EasyHighJavaScript

Coding

Sleep / Delay Promise

Implement sleep(ms) that returns a Promise resolving after ms milliseconds. Use it to pause async flows like retries, ex…

EasyHighJavaScript

Coding

Update Array at Index (Immutable)

Return a new array with one index updated, leaving the original array untouched. This is the core immutable update patte…

EasyHighJavaScript

Coding

Create a Deferred Promise (For Async Tests)

Implement createDeferred() to build a controllable Promise: { promise, resolve, reject }. This is a common testing tool…

IntermediateHighJavaScript

Coding

Create a Spy Function (Test Double)

Implement createSpy(impl?) to produce a callable spy that records every call (args + this) and optionally delegates to a…

IntermediateHighJavaScript

Coding

Data Helper 1: Get Value by Path

Implement `getByPath(obj, path, fallback?)` that safely reads a nested value from an object. This is extremely common in…

IntermediateHighJavaScript

Coding

Fetch JSON with Timeout + Abort

Implement fetchJson(url, options) that fetches JSON with built-in timeout and abort support. It should abort on timeout,…

IntermediateHighJavaScript

Coding

Fluid Type & Spacing with clamp()

Implement fluid typography and spacing with `clamp()`. Use `clamp(min, preferred, max)` to scale values across viewport…

IntermediateHighCSS

Coding

Forms: Validation and Required Fields

Build a signup form using native HTML5 validation: required fields, type constraints, minlength, and pattern. The browse…

IntermediateHighHTML

Coding

Implement `instanceof`

Recreate `instanceof` by walking the prototype chain and checking if it reaches `Constructor.prototype`. Handle null/pri…

IntermediateHighJavaScript

Coding

Promise.any (First Fulfilled)

Implement promiseAny(promises) that behaves like Promise.any. It should resolve with the first fulfilled value, ignoring…

IntermediateHighJavaScript

Coding

Run With a Performance Budget (Sync or Async)

Implement runWithPerfBudget(fn, budgetMs, now?) to time a sync or async function and report whether it stayed within a b…

IntermediateHighJavaScript

Coding

Sanitize href URL (Block javascript: XSS)

Implement sanitizeHrefUrl(input) to safely use user-provided URLs in an <a href="...">. Use an allowlist for safe scheme…

IntermediateHighJavaScript

Coding

Take Latest (Abort Previous Requests)

Implement takeLatest(fn) that wraps an async function and guarantees only the most recent call can resolve. Each new cal…

IntermediateHighJavaScript

Coding

Implement Function.prototype.bind

Implement `myBind(fn, thisArg, ...boundArgs)` that behaves like `Function.prototype.bind`. It must: 1) Bind `this` to `t…

HardHighJavaScript

Coding

Implement the `new` Operator

Implement a myNew helper that mimics the new operator. Create an object linked to the constructor prototype, call the co…

HardHighJavaScript

Coding

Check if Two Arrays Are Equal

Check whether two arrays are equal by length and by value at each index. This is a shallow equality check for primitive…

EasyMediumJavaScript

Coding

Cleanup Bag (Dispose Subscriptions)

Implement createCleanupBag() that helps prevent memory leaks by tracking cleanup functions (like removing event listener…

EasyMediumJavaScript

Coding

Create a Counter Function

Support an optional initial value and keep the API simple so consumers can call inc/dec/get without exposing the interna…

EasyMediumJavaScript

Coding

Create Object with Prototype

Implement objectCreate(proto) to return a new object whose prototype is `proto`. Use a temporary constructor function or…

EasyMediumJavaScript

Coding

Display & Centering: Center Inline Content

This is a horizontal alignment task, so avoid flex unless vertical alignment is explicitly required by the prompt. Use t…

EasyMediumCSS

Coding

Escape HTML for Safe Text

Implement escapeHtml(text) to convert &, <, >, " and ' into HTML entities so user-provided text can be safely inserted i…

EasyMediumJavaScript

Coding

Falsy Bouncer

Remove all falsy values from an array while preserving order. Use a boolean filter to drop false, 0, empty string, null,…

EasyMediumJavaScript

Coding

Flatten One Level

This should not deep-flatten; only the first nesting level is removed, matching Array.prototype.flat(1). Use it to norma…

EasyMediumJavaScript

Coding

Inline vs Block Elements

Demonstrate the difference between block and inline elements using pure HTML. Show that block elements start new lines w…

EasyMediumHTML

Coding

Lists and Navigation

Build a semantic navigation bar using `nav > ul > li > a` with hash links. Use CSS `:target` to show only one section at…

EasyMediumHTML

Coding

Once (Function Wrapper)

Implement once(fn) that returns a wrapper which executes `fn` only on the first call. Cache and return the result on sub…

EasyMediumJavaScript

Coding

Querystring Helper 1: Implement `parseQueryString`

Implement `parseQueryString(qs)` that converts a URL querystring into a plain object. This is very common in frontend wo…

EasyMediumJavaScript

Coding

Selectors & Text: Hero Title + Lead + Emphasis (Interview Warm-up)

Style a small hero header using both element and class selectors. Establish base typography on element selectors, then o…

EasyMediumCSS

Coding

Todo List (Component with Local State)

Create a local-state todo list: add, toggle, and remove items. Keep input state controlled, generate stable ids, and upd…

EasyMediumReact

Coding

Format Date in Time Zone (YYYY-MM-DD)

Implement formatDateInTimeZone(date, timeZone) to return a YYYY-MM-DD string for a given Date (or timestamp) in a specif…

IntermediateMediumJavaScript

Coding

Implement arrayForEach (no prototype mutation)

You should also ensure the callback is invoked with the correct thisArg and that the method returns undefined like the n…

IntermediateMediumJavaScript

Coding

Measure Function Duration (Profiling Wrapper)

Implement measure(fn, now?) to profile execution time. It should run a function, measure the duration using the provided…

IntermediateMediumJavaScript

Coding

Poll Until (with Timeout + Abort)

Implement pollUntil(check, { interval, timeout, signal }) that repeatedly runs a check until it returns a truthy value.…

IntermediateMediumJavaScript

Coding

Storage TTL Cache (localStorage/sessionStorage)

Implement createTtlStorage(storage, now?) that returns { set, get, remove }. It should store JSON values with an optiona…

IntermediateMediumJavaScript

Coding

Stream to Text (ReadableStream -> string)

Implement streamToText(stream, options) that reads a ReadableStream<Uint8Array> and returns the full string. Use TextDec…

IntermediateMediumJavaScript

Coding

Transitions & Transforms: Lift on Hover

Create a hover lift effect with `transform` and `transition`. Combine a slight translate/scale with a deeper `box-shadow…

IntermediateMediumCSS

Coding

Create an LRU Cache (Bounded Memory)

Implement createLruCache(maxSize) to keep a bounded, eviction-based cache. This is a classic way to prevent "memory leak…

HardMediumJavaScript

Coding

Capitalize Words

Capitalize the first letter of every word while preserving spacing. Handle multiple spaces and punctuation without colla…

EasyMediumJavaScript

Coding

Check if an Object or Array is Empty

Implement `isEmpty(obj)` that returns `true` only if the input is an object or array with no own keys/elements, and `fal…

EasyMediumJavaScript

Coding

Clamp

Implement clamp(value, lower, upper) to keep a number within an inclusive range. If the value is below the lower bound,…

EasyMediumJavaScript

Coding

Count Vowels

Implement countVowels(str) that returns how many vowels appear in a string. Normalize case, decide whether to include 'y…

EasyMediumJavaScript

Coding

React Counter (Guarded Decrement)

Build a React counter component with increment/decrement and a zero floor. Use state for the count, disable decrement at…

EasyMediumReact

Coding

Safe JSON Parse (Fallback on Error)

Implement safeJsonParse(text, fallback = null) to safely parse JSON. It should return the parsed value for valid JSON st…

EasyMediumJavaScript

Coding

Sum of Numbers in an Array

Sum only numeric values from an input array, ignoring non-numbers and `NaN`. This reinforces safe type checking, accumul…

EasyMediumJavaScript

Coding

Validate Username (Rules + Edge Cases)

Implement validateUsername(name) to enforce common username rules and handle edge cases safely. Rules: 3–16 chars, lower…

EasyMediumJavaScript

Coding

Warm-Up: Basic Structure

Build a valid HTML document skeleton with `<!doctype html>`, `<html>`, `<head>`, and `<body>`. Include a `<meta charset>…

EasyMediumHTML

Coding

Resolve package.json Exports (Import vs Require)

Implement resolvePackageEntry(pkg, options) to choose the correct entry file for a package based on package.json fields…

HardMediumJavaScript

Coding

Debug: Component Renders Twice on Every Update

Locked

Fix a component that renders twice per click because it stores derived state in `useEffect`. The correct fix is to remov…

IntermediateHighReact

Coding

React Debounced Search with Fake API

Locked

Build a React debounced search input with fake API calls. Use useEffect + setTimeout cleanup to cancel stale requests, a…

IntermediateHighReact

Coding

Reusable Child Component with @Input/@Output (Two-way Binding)

Locked

Expose a value input and a valueChange output to support two-way binding, and keep the child component stateless so the…

IntermediateHighAngular

Coding

useEffectOnce: Run an Effect Only Once

Locked

This hook should run the effect only on mount and clean up on unmount, even under React StrictMode development behavior.…

IntermediateHighReact

Coding

Remove Duplicates

Locked

Implement uniqueArray(arr) that removes duplicates while preserving order. Use a Set for O(n) time and clarify how to tr…

EasyHighJavaScript

Coding

Sort Numbers with Array.prototype.sort

Locked

Implement a function `sortNumbers(arr, ascending = true)` that returns a **new array** of numbers sorted numerically in…

EasyHighJavaScript

Coding

Autocomplete Search Bar (Hooks)

Locked

Build an **autocomplete search bar** in React. As the user types, show a dropdown of suggestions filtered from a dataset…

IntermediateHighReact

Coding

Contact Form (Component + HTTP)

Locked

Build a contact form using a React component with controlled inputs and basic validation. You will only work in `src/App…

IntermediateHighReact

Coding

Custom setTimeout/clearTimeout Timer Manager

Locked

Build a timer registry with mySetTimeout, myClearTimeout, and myClearAllTimeouts. Return your own numeric ids, store nat…

IntermediateHighJavaScript

Coding

Data Helper 2: Set Value by Path

Locked

Implement setByPath(obj, path, value) that returns a new object/array tree with the value written at the nested path. No…

IntermediateHighJavaScript

Coding

Delegated Event Handler (E)

Locked

Implement `delegate(root, eventType, selector, handler)` for **event delegation**. Requirements: 1) Attach **one** event…

IntermediateHighJavaScript

Coding

Event Emitter (Mini Implementation)

Locked

Build a tiny event emitter with on, off, and emit. Store listeners per event, allow multiple listeners, and ensure off r…

IntermediateHighJavaScript

Coding

Group By

Locked

Group an array of items by a key (function or property). Build an object or Map where each key maps to an array of items…

IntermediateHighJavaScript

Coding

Implement Array.prototype.filter

Locked

Recreate the native `Array.prototype.filter()` method as `myFilter`. It should call a provided callback once for each ex…

IntermediateHighJavaScript

Coding

Implement Array.prototype.map

Locked

Recreate the native `.map()` method **without using it**. Your `myMap` must call `callbackFn(value, index, array)` for e…

IntermediateHighJavaScript

Coding

Implement Array.prototype.reduce

Locked

Recreate the native `.reduce()` method **without using it**. Your `myReduce` must call the reducer with `(accumulator, c…

IntermediateHighJavaScript

Coding

Implement lodash.get

Locked

Implement `get(obj, path, defaultValue)` where `path` is a string like `user.profile.name` or `a[0].b`. Return `defaultV…

IntermediateHighJavaScript

Coding

Implement Promise.all

Locked

Implement a function `promiseAll(promises)` that behaves like `Promise.all`. It should take an array of values or promis…

IntermediateHighJavaScript

Coding

Invite Chips Input (Tags + Autocomplete)

Locked

Build a Material-like invite field in React. As users type, show autocomplete suggestions, convert selections into remov…

IntermediateHighReact

Coding

Memoization

Locked

Implement memoize(fn) that caches results for repeated calls. Choose a cache key strategy, discuss memory growth/evictio…

IntermediateHighJavaScript

Coding

Modal: Native <dialog> Confirm (Accessible Naming)

Locked

Build a native confirm dialog for deleting a project using the HTML <dialog> element. The dialog must be accessible (pro…

IntermediateHighHTML

Coding

Multi-step Signup Form

Locked

Build a 3-step signup flow in React that collects basic info, address info, and then shows a read-only summary before su…

IntermediateHighReact

Coding

React Nested Checkbox Tree (Parent–Child Sync)

Locked

Build a small React UI that renders a parent checkbox and multiple child checkboxes. The parent controls all children, a…

IntermediateHighReact

Coding

React Nested Comments (Infinite Replies, Single Active Reply Input)

Locked

Build a React nested comments panel with infinite replies. Users can add top-level comments and reply to any comment, cr…

IntermediateHighReact

Coding

React Paginated Data Table

Locked

Build a simple paginated data table in React that shows a static list of users. Display 5 rows per page, with Previous /…

IntermediateHighReact

Coding

React Shopping Cart Mini

Locked

Build a small shopping cart UI in React. Show a list of products, let the user add them to the cart, adjust quantities,…

IntermediateHighReact

Coding

Throttle Function

Locked

Implement a function `throttle(fn, interval)` that ensures `fn` is executed at most once during every `interval` millise…

IntermediateHighJavaScript

Coding

Chat UI with Streaming Response

Locked

Build a simplified ChatGPT-like interface that streams an assistant response token-by-token. The goal is to model chat s…

HardHighReact

Coding

Concurrency-Limited Map (order-preserving)

Locked

Implement a concurrency-limited async map that preserves order. Run at most N promises at a time, resolve results in inp…

Create a deep clone of an object/array so nested structures are copied by value. Discuss limits (functions, dates, cycle…

Implement a function `deepEqual(a, b)` that returns `true` when two values are deeply equal — primitives by value and ob…

HardHighJavaScript

Coding

Delegated Event Handler (M)

Locked

Implement `delegate(root, eventType, selector, handler, options?)` with **advanced event delegation**. Requirements: 1)…

HardHighJavaScript

Coding

Querystring Helper 3: Implement `parseQueryStringAdvanced`

Locked

Implement `parseQueryStringAdvanced(qs)` that converts a URL querystring into a **nested** object structure. This mirror…

HardHighJavaScript

Coding

Add Large Integers as Strings

Locked

Add two non-negative integers represented as strings and return the sum as a string. You may not convert the entire stri…

EasyMediumJavaScript

Coding

Find Maximum Occurring Character

Locked

Find the most frequent character in a string using a frequency map. Track counts in one pass and return the character wi…

EasyMediumJavaScript

Coding

Image Slider (Dots + Previous/Next)

Locked

Build a simple React image slider with previous/next buttons and dot navigation. Show the current slide, its title, and…

EasyMediumReact

Coding

Merge Two Sorted Arrays

Locked

Merge two already-sorted arrays into a single sorted array. Do not call sort on the combined output; use a two-pointer m…

Reverse a string by iterating from the end to the start and building a new string, without using `Array.prototype.revers…

EasyMediumJavaScript

Coding

Selector Polyfill 1: Implement `matchesSimple`

Locked

Implement `matchesSimple(node, selector)` — a tiny subset of `Element.matches()`. This is extremely common in frontend i…

EasyMediumJavaScript

Coding

3Sum (find unique triplets that sum to zero)

Locked

Given an array of integers, return all unique triplets `[a, b, c]` such that `a + b + c = 0`. Triplets should be unique,…

IntermediateMediumJavaScript

Coding

Add Two Promises

Locked

This is a small async composition task and should return a Promise that resolves to the numeric sum once both inputs set…

IntermediateMediumJavaScript

Coding

Build a DOM Renderer from a Nested Object

Locked

Implement render(node) to convert a JSON-like DOM description into real DOM nodes using createElement/createTextNode. Co…

IntermediateMediumJavaScript

Coding

Clear All Timers + Render DOM Elements

Locked

Solve two independent tasks: implement clearAllTimeouts for a timer registry and render a DOM tree from a nested object.…

IntermediateMediumJavaScript

Coding

Compose Function

Locked

Implement `compose(...fns)` that returns a new function applying the provided functions from **right to left**. The righ…

IntermediateMediumJavaScript

Coding

Curry Function

Locked

Implement curry(fn) to transform a multi-argument function into chained calls. Collect arguments across invocations, all…

IntermediateMediumJavaScript

Coding

DOM Tree Walk 2: Find Closest Ancestor

Locked

Implement `closestWithin(node, selector, boundary)` for a **DOM-like** tree. This is a simplified `.closest()` used cons…

IntermediateMediumJavaScript

Coding

Find a Node in a DOM Tree (DFS/BFS)

Locked

Implement findNode(root, predicate) to traverse the DOM and return the first matching element. Use DFS/BFS with early ex…

IntermediateMediumJavaScript

Coding

Find the Corresponding Node in Twin DOM Trees

Locked

Given two identical DOM trees and a node in tree A, return the corresponding node in tree B. Traverse both trees in sync…

IntermediateMediumJavaScript

Coding

Flatten with Depth

Locked

Implement flatten(arr, depth) that flattens nested arrays up to a specific depth. Depth controls how many nesting levels…

IntermediateMediumJavaScript

Coding

Querystring Helper 2: Implement `stringifyQueryString`

Locked

Implement `stringifyQueryString(params)` that converts an object into a URL querystring. This is common in FE screens (b…

IntermediateMediumJavaScript

Coding

React Accordion / FAQ Component

Locked

Build a simple FAQ (accordion) UI in React using component state. Clicking a question should toggle its answer. By defau…

IntermediateMediumReact

Coding

React Filterable / Searchable User List

Locked

Filter a React user list by search text and role. Derive filtered results without mutating the source array, and show an…

IntermediateMediumReact

Coding

React Transfer List (Select + Move Between Two Lists)

Locked

Build a React transfer list UI with two panels and checkbox selection. Users select items in one list and move them to t…

IntermediateMediumReact

Coding

Selector Polyfill 2: Implement `closestSimple`

Locked

Implement `closestSimple(node, selector)` — a DOM-like polyfill for `Element.closest()` using **only** `parentNode` trav…

IntermediateMediumJavaScript

Coding

Abortable Helpers (Timeout + Composed Abort)

Locked

Provide utilities to combine timeouts with AbortController, and to compose multiple signals (abort if any fires). All he…

HardMediumJavaScript

Coding

Data Helper 3: Deep Clone with Cycles

Locked

Implement `deepClone(value)` that returns a **deep copy** of the input while correctly handling **circular references**.…

HardMediumJavaScript

Coding

Delegated Event Handler (H)

Locked

Implement delegated event handling: attach one listener to a parent, match events by selector, and call the handler with…

HardMediumJavaScript

Coding

React Snake Game (Grid + Food + Collision)

Locked

Build a Snake game in React using a grid board. Support keyboard controls, food spawning, score updates, and game-over h…

HardMediumReact

Coding

Streaming NDJSON Parser (Web Streams)

Locked

Build an NDJSON streaming parser that reads chunked text and emits JSON objects line by line. Handle partial lines acros…

HardMediumJavaScript

Coding

Angular Chessboard Click/Highlight (N×N Board)

Locked

Build an interactive N×N chessboard in Angular. Clicking a cell should highlight it and clear the previous selection. Ad…

Return the median of a list of numbers. For even length, return the average of the two middle values. Do not mutate the…

EasyMediumJavaScript

Coding

React Chessboard Click/Highlight (N×N Board)

Locked

Build an interactive N×N chessboard in React. Clicking a cell should highlight it and clear the previous selection. Incl…

EasyMediumReact

Coding

React Dynamic Table (Rows × Columns)

Locked

Generate a dynamic table in React from row/column inputs. Normalize values, rebuild the grid on action, and render consi…

EasyMediumReact

Coding

React Like Button (Toggle + Counter)

Locked

Build a React Like button that toggles between liked/unliked and updates a count. Clicking should add or subtract one ba…

EasyMediumReact

Coding

React Progress Bar (0–100 with Threshold Colors)

Locked

Build a React progress bar for values 0–100 with +10%/−10% controls. Clamp progress to the valid range and change the ba…

EasyMediumReact

Coding

React Star Rating Widget

Locked

Implement a reusable <StarRating /> widget in React. It should render a row of clickable stars, allow the user to select…

EasyMediumReact

Coding

Tic-Tac-Toe (Component State + Winner Detection)

Locked

Build Tic-Tac-Toe with React state: a 9-cell board, alternating turns, win/draw detection, and a reset button. Prevent o…

Return true if two strings are anagrams (same characters with the same counts). Treat strings as case-sensitive and incl…

EasyMediumJavaScript

Coding

Vue Chessboard Click/Highlight (N×N Board)

Locked

Build an interactive N×N chessboard in Vue 3. Clicking a cell should highlight it and clear the previous selection. Add…

EasyMediumVue

Coding

DOM Tree Walk 1: Collect Text Nodes

Locked

Implement `collectText(node)` that traverses a **DOM-like** tree and returns **all text content** (nodeType `3`) in **do…

IntermediateMediumJavaScript

Coding

Implement Stack and Queue in JavaScript

Locked

Implement Stack (push/pop/peek/size) and Queue (enqueue/dequeue/peek/size). Use a head index or deque to keep queue oper…

IntermediateMediumJavaScript

Coding

Maze Traversal (Find a Path in a Grid)

Locked

Given a 2D grid of 0/1 (0=open, 1=wall), determine if a path exists from start to end using 4-direction moves. Use BFS/D…

IntermediateMediumJavaScript

Coding

React Dynamic Counter Buttons (Grow-on-Click)

Locked

In React, let users add or remove step buttons dynamically, and have each button update the counter by its own step valu…

IntermediateMediumReact

Coding

React Tabs / Multi-View Switcher

Locked

Implement React tabs with a single activeTab state. Buttons update the value and conditional rendering shows only the ac…

IntermediateMediumReact

Coding

React Theme Toggle with Persisted Light/Dark Mode

Locked

Add a global light/dark theme toggle using React Context. The selected theme should be stored in localStorage and restor…

IntermediateMediumReact

Coding

Recover a BST with Two Swapped Nodes

Locked

Two nodes in a Binary Search Tree were swapped by mistake. Implement `recoverBST(root)` to fix the tree **in-place** (sw…

IntermediateMediumJavaScript

Coding

DOM Tree Walk 3: Basic Selector Engine (Hard)

Locked

Implement a small selector engine: `queryAll(root, selector)` that returns all matching nodes in **document order** from…

HardMediumJavaScript

Coding

Selector Polyfill 3: Implement `queryAllSimple` (Hard)

Locked

Implement `queryAllSimple(root, selector)` — a DOM-like polyfill for `querySelectorAll`. This is a high-likelihood front…

HardMediumJavaScript

Coding

Check if a String Is a Palindrome

Locked

Normalize the input (lowercase + strip non-alphanumerics) and check if it reads the same forwards and backwards using tw…

EasyLowJavaScript