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TypeScript Interview Questions

380+ most important TypeScript interview questions on library APIs, utility types, algorithms, and building strong, typed components.
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TypeScript Interview GuidesExplore our starter guides to get a solid grasp of TypeScript interview prep before jumping into practice.
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GUIDES
  • Make CounterImplement a function that accepts an integer value and returns a function that can be repeatedly called to return increasing values
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  • MeanImplement a function that finds the mean of the values inside an array
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  • Function.prototype.callImplement the Function.prototype.call() function that calls the function with a given `this` value and provided arguments
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  • Min ByImplement a function that finds the minimum element based on the specified criteria
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  • Selection SortImplement a function that performs a selection sort
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  • StackImplement a stack data structure containing the common stack methods
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  • Type UtilitiesImplement utilities to determine primitive variable types in JavaScript
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  • Array.prototype.reduceImplement the Array.prototype.reduce() method
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  • Count Set Bits in a Binary NumberImplement a function to find set bits in binary representation of a given integer
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  • CycleImplement a function that takes one or more values and returns a function that cycles through those values each time it is called
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  • Find Duplicates in ArrayImplement a function to check if there are any duplicate numbers in the array
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  • Find Missing Number in SequenceImplement a function to find the missing element in a sorted array
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  • Insertion SortImplement a function that performs an insertion sort
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  • Optimal Stock TradingImplement a function to find the maximum profit achievable by buying and selling a stock once
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  • Pair sumImplement a function to find two numbers within an array of integers that add up to a target integer
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  • String AnagramImplement a function to determine if two strings are anagram of each other
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  • Type Utilities IIImplement utilities to determine non-primitive variable types in JavaScript
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  • Binary Tree Maximum DepthImplement a function to find the maximum depth of a binary tree
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  • Flip Binary TreeImplement a function to flip the nodes in a binary tree
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  • Staircase Climbing CombinationsImplement a function to find the number of ways to reach at the top of staircase
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  • Balanced BracketsImplement a function to determine if a string contains balanced brackets
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  • Binary Tree EqualImplement a function to determine whether two binary trees are equal
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  • Bit CountingImplement a function to find number of set bits from 0 to n
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  • Bit ReversalImplement a function to flip the order of the bits in a given number
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  • Linked List ReversalImplement a function to reverse a linked list
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  • String PalindromeImplement a function to determine if a string is a palindrome
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  • Linked List Detect CycleImplement a function to detect if there are cycles in a linked list
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  • Binary Tree SubtreeImplement a function to check if a binary tree is a subtree of another binary tree
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  • Linked Lists Combine Two SortedImplement a function to combine two sorted linked list
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  • Meeting CalendarImplement a function to check if all meetings can be attended
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  • Array Product Excluding CurrentImplement a function to find the product of elements in an array excluding the current element
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  • Binary SearchImplement a function that performs binary search on an array of numbers
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  • Breadth-first SearchImplement a breadth-first search algorithm that traverses a directed graph in a breadth-first manner
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  • Count ByImplement a function that counts the number of times a value appears in an array based on a function or property name
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  • CurryImplement a function that transforms a function that takes multiple arguments into a function that can be repeatedly called with only one argument at a time
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  • DebounceImplement a function to limit how many times a function can be executed by delaying the execution of the function until after a specified time after its last execution attempt
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  • Depth-first SearchImplement a depth-first search algorithm that traverses a directed graph in a depth-first manner
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  • Heap SortImplement a function that performs a heap sort
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  • Is the Graph a TreeImplement a function to determine if a graph is a valid tree
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  • Maximum Water Trapped Between WallsImplement a function to find the maximum water volume between two walls in an array of walls
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  • PromisifyImplement a function that takes a function following the common error-first callback style and returns a version that returns promises
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  • QueueImplement a queue data structure containing the common queue methods
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  • ThrottleImplement a function to control the execution of a function by limiting how many times it can execute over time
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  • ClassnamesImplement a function that conditionally joins CSS class names together
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  • Data MergingImplement a function to merge rows of data from the same user
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  • Event EmitterImplement a class that can subscribe to and emit events that trigger attached callback functions
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  • FlattenImplement a function that recursively flattens an array into a single level deep
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  • getElementsByStyleImplement a function to get all DOM elements that are rendered using the specified style
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  • HTML SerializerImplement a function to serialize an object into an HTML string with indentation
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  • JSON.stringifyImplement a function that converts a JavaScript value into a JSON string
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  • List FormatImplement a function that formats a list of items into a single readable string
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  • MemoizeImplement a function that returns a memoized version of a function which accepts a single argument
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  • Merge SortImplement a function that performs a recursive merge sort
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  • Promise.allImplement the Promise.all() function that resolves to an array of results if all the input elements are resolved or rejects otherwise
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  • Promise.anyImplement the Promise.any() function that resolves when any of the input elements are resolved
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  • Quick SortImplement a function that performs a recursive quick sort
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  • Squash ObjectImplement a function that returns a new object after squashing the input object into a single level of depth
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  • Topological SortImplement a function that performs a topological sort
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  • Binary Tree Level Order TraversalImplement a function to find the level order traversal of a binary tree
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  • Deep CloneImplement a function that performs a deep copy of a value
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  • Deep EqualImplement a function that determines if two values are equal
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  • getElementsByClassNameImplement a function to get all DOM elements that contain the specified classes
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  • Map Async LimitImplement a function that maps an array of items with an asynchronous mapping function while not exceeding the concurrency limit
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  • Maximum Sum in Contiguous ArrayImplement a function to find the subarray with the maximum sum
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  • Smallest element in rotated sorted arrayImplement a function to find the smallest element in rotated sorted array
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  • Deep OmitImplement a function that removes specified keys and their corresponding values from an object, including nested objects or arrays
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  • Find Element in Rotated ArrayImplement a function to find an integer in a rotated sorted array
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  • Maximum Product in Contiguous ArrayImplement a function to find the subarray which has the largest product
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  • Binary Search Tree Kth Smallest ElementImplement a function to find the kth smallest node in a BST
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  • Binary Search Tree Lowest Common AncestorImplement a function to find the LCA in a binary search tree
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  • Count Islands in a GridImplement a function to count distinct islands in a 2D binary grid
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  • Delete Nth Node from End of Linked ListImplement a function to delete the nth node from the end of a linked list
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  • Distinct Paths in GridImplement a function to calculate distinct paths for a robot moving on an m x n grid
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  • Matrix ZeroingImplement a function to set matrix rows and columns to zero
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  • Merge Overlapping IntervalsImplement a function to merge overlapping intervals
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  • Most Common ElementsImplement a function to determine the most common elements in an integer array
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  • Neighborhood TheftImplement a function to find maximum money to rob without alerting police
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  • Rearrange Linked ListImplement a function to rearrange the nodes in a linked list
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  • Sum Without AdditionImplement a function to find the sum of two integers without using + and - operator
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  • Triplet SumImplement a function to find all unique triplets with distinct indices that sum to 0
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  • Validate Binary Search TreeImplement a function to validate whether a binary tree is a valid binary search tree
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  • Combinations for Target SumImplement a function to count combinations that sum to the target
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  • Course DependencyImplement a function to check if all courses can be completed given prerequisites
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  • Decode MessageImplement a function to count ways to decode a numeric string
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  • Longest Consecutive Number SequenceImplement a function to find the length of the longest consecutive number sequence
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  • NEW
    Longest Increasing SubsequenceImplement a function to find the length of the longest increasing subsequence
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  • NEW
    Minimum Coins for ChangeImplement a function to return minimum coins needed to make the given amount
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  • Palindromic SubstringsImplement a function to count all palindromic substrings in a string
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  • Segment WordsImplement a function to check whether a string be formed from dictionary words
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  • String Anagram GroupsImplement a function to group an array of strings into anagrams
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  • Task CoordinationImplement a function to find minimum intervals for tasks with cooldown
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  • Trie (Prefix Tree)Implement a trie-prefix-tree with insert, search, and starts with functionality
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  • Binary Tree Rebuilding from Preorder and Inorder TraversalsImplement a function to construct a binary tree from preorder and inorder traversals
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  • Disjoint IntervalsImplement a function to determine the minimum amount of removals to get non-overlapping intervals
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  • End of Array ReachableImplement a function to determine if the end of the array is reachable
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  • Find the Longest Palindromic SubstringImplement a function to find the longest palindromic substring
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  • Find Word in GridImplement a function to check the existence of a word in a grid
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  • Graph Count Connected ComponentsImplement a function to count connected components in a graph
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  • Longest Common SubsequenceImplement a function to find the longest common subsequence in two strings
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  • Longest Non-repeating SubstringImplement a function to find the length of longest substring with unique characters
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  • Longest Repeating Substring After ReplacementsImplement a function to find the longest uniform substring after up to k replacements
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  • Matrix RotationImplement a function to rotate the given matrix by 90 degrees
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  • Matrix Spiral TraversalImplement a function to traverse the matrix in spiral order
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  • Merge New IntervalImplement a function to insert a new interval in the given intervals
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  • Neighborhood Theft (Circular)Implement a function to find maximum money to rob in circular houses without alerting police
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  • Ocean FlowImplement a function returning cells with water flow to both oceans
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  • Word FinderImplement a data structure where words can be added and support wildcard searching
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  • Graph CloneImplement a function to deeply clone a connected and undirected graph
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  • Minimum Meeting Rooms NeededImplement a function to find the minimum number of required conference rooms
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  • Binary Tree Serialization and DeserializationImplement a function to serialize and deserialize a binary tree
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  • Binary Tree Maximum Total PathImplement a function to find the maximum total of nodes in a binary tree path
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  • Find Words in GridImplement a function to find all the words present in the grid
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  • Linked Lists Combine K SortedImplement a function to combine k sorted linked lists
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  • Shortest Substring Containing CharactersImplement a function to return the smallest substring of a string containing all characters from another string
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  • Extraterrestrial LanguageImplement a function to verify and return an extraterrestrial language's alphabet order
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  • Number Stream MedianImplement a function to find the median of a dynamic stream of integers
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  • ClampPremiumImplement a function to clamp a number within the inclusive lower and upper bounds
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  • Function LengthPremiumImplement a function that returns the number of parameters expected by a function
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  • Number of ArgumentsPremiumImplement a function that returns the number of arguments it was called with
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  • SleepPremiumImplement a function that pauses for a specified duration before resuming execution
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  • Array.prototype.squarePremiumImplement a custom Array.prototype.square() method that squares the values in an array
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  • Cancellable IntervalPremiumImplement a function that acts like setInterval but returns a function to cancel the interval
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  • Cancellable TimeoutPremiumImplement a function that acts like setTimeout but returns a function to cancel the pending callback
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  • ChunkPremiumImplement a function that creates an array of elements split into smaller groups of a specified size
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  • CompactPremiumImplement a function that creates an array with all falsey values removed
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  • DifferencePremiumImplement a function that finds the difference in values between arrays
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  • Drop Right WhilePremiumImplement a function that excludes elements from the end of an array until the predicate returns false
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  • Drop WhilePremiumImplement a function that excludes elements from the beginning of an array until the predicate returns false
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  • FillPremiumImplement a function that fills an array with values within specified indices
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  • Find IndexPremiumImplement a function that returns the index of the first element in the array that satisfies the provided testing function
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  • Find Last IndexPremiumImplement a function that returns the index of the last element in the array that satisfies the provided testing function
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  • From PairsPremiumImplement a function that returns an object composed from key-value pairs
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  • Function.prototype.applyPremiumImplement the Function.prototype.apply() function that calls the function with a given `this` value and arguments as an array
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  • GetPremiumImplement a function to safely access deeply-nested properties in JavaScript objects
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  • In RangePremiumImplement a function to check if a number falls between two numbers
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  • IntersectionPremiumImplement a function that computes the intersection of arrays, returning a new array containing unique values present in all given arrays
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  • Max ByPremiumImplement a function that finds the maximum element based on the specified criteria
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  • Object MapPremiumImplement a function to transform values within an object
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  • OncePremiumImplement a function that accepts a callback and restricts its invocation to at most once
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  • Promise.rejectPremiumImplement a function to return a Promise object rejected with a reason
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  • RangePremiumImplement a function that returns a sequence of numbers in ascending order
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  • Range RightPremiumImplement a function that returns a sequence of numbers in descending order
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  • SingletonPremiumImplement a Singleton class that ensures a class has only one instance while providing a global point of access to that instance
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  • Unique ArrayPremiumImplement a function to remove all duplicate values from an array
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  • Array.prototype.atPremiumImplement the Array.prototype.at() method
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  • Array.prototype.filterPremiumImplement the Array.prototype.filter() method
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  • Array.prototype.mapPremiumImplement the Array.prototype.map() method
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  • ComposePremiumImplement a function that takes multiple functions as arguments and returns a new function that applies those functions in reverse
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  • Function.prototype.bindPremiumImplement the Function.prototype.bind() function that creates a new function with the `this` keyword set to a provided value
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  • jQuery.cssPremiumImplement a jQuery-like function that sets the style of a DOM element
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  • Promise.racePremiumImplement the Promise.race() function that resolves or rejects when any of the input elements are resolved or rejected
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  • SizePremiumImplement a function that returns the size of collection
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  • SumPremiumImplement a function that sums numbers by accepting a number and allows for repeated calling with more numbers until it is not called with any number
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  • Make Counter IIPremiumImplement a function that returns a counter object with methods to retrieve and manipulate the value
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  • Array.prototype.concatPremiumImplement the Array.prototype.concat() method
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  • Group ByPremiumImplement a function that groups values in an array based on a function or property name
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  • Intersection ByPremiumImplement a function that returns an array of unique values that are included in all given arrays based on a provided iteratee function
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  • Intersection WithPremiumComputes the intersection of arrays using a custom comparator function to determine equality between elements
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  • Is EmptyPremiumImplement a function to check if a value is an empty object, collection, map, or set
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  • LimitPremiumImplement a function that accepts a callback and restricts its invocation to at most N times
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  • Promise MergePremiumImplement a function to merge the results of two promises into a single value
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  • Promise TimeoutPremiumImplement a function that resolves a promise if it is fulfilled within a timeout period and rejects otherwise
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  • Promise.resolvePremiumImplement a function to resolve a given value to a Promise
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  • Promise.withResolversPremiumImplement a function that returns an object containing a new `Promise` object and two functions to resolve or reject it
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  • Promisify IIPremiumImplement a promisify function that allows the original function to override the return value
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  • TurtlePremiumImplement a Turtle class that moves a turtle on a 2D plane
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  • Union ByPremiumImplement a function that creates an array of unique values, in order, from all given arrays.
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  • Camel Case KeysPremiumImplement a function to convert all the keys in an object to camel case
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  • Compact IIPremiumImplement a function that returns an object with all falsey values removed
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  • Conforms ToPremiumImplement a function that checks if object conforms to source
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  • Curry IIPremiumImplement a function that transforms a function that takes multiple arguments into a function that can be repeatedly called with any number of arguments
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  • Debounce IIPremiumImplement a debounce function that comes with a cancel method to cancel delayed invocations and a flush method to immediately invoke them
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  • Event Emitter IIPremiumImplement a class that can subscribe to and emit events that trigger attached callback functions. Subscription objects are returned and can unsubscribe itself
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  • getElementsByTagNamePremiumImplement a function to get all DOM elements that match a tag
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  • Identical DOM TreesPremiumImplement a function to determine if two DOM trees are the same
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  • jQuery Class ManipulationPremiumImplement a set of jQuery-like functions that manipulates classes on a DOM element
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  • Map AsyncPremiumImplement a function that maps an array of items with an asynchronous mapping function
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  • Promise.allSettledPremiumImplement the Promise.allSettled() function that resolves to an array of outcomes when all the input elements are either resolved or rejected
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  • Resumable IntervalPremiumImplement a function that creates a resumable interval object
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  • Text SearchPremiumImplement a function to highlight text if a searched term appears within it
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  • Deep MapPremiumImplement a function to recursively transform values
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  • Text Search IIPremiumImplement a function to highlight text if searched terms appear within it
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  • Deep MergePremiumImplement a function that merges two objects together
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  • Memoize IIPremiumImplement a function that returns a memoized version of a function which accepts any number of arguments
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  • Curry IIIPremiumImplement a function which transforms a function which takes variadic arguments into a function that can be repeatedly called with any number of arguments
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  • Classnames IIPremiumImplement a function that conditionally joins CSS class names together and also handles de-duplication and function values
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  • Backbone ModelPremiumImplement a class resembling Backbone.Model which allows storing of attributes/values and responding to changes in specific attribute values
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  • Data SelectionPremiumImplement a function to filter rows of data matching a specified requirement
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  • getElementsByTagNameHierarchyPremiumImplement a function to get all DOM elements that match a tag hierarchy
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  • Table of ContentsPremiumImplement a function to construct a table of contents from an HTML document
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  • Deep Clone IIPremiumImplement a function that performs a deep copy of a value, but also handles circular references
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  • JSON.stringify IIPremiumImplement a function that converts a JavaScript value into a JSON string
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TypeScript Interview Questions and Answers

Tired of sifting through poor-quality resources for TypeScript interview preparation? Our comprehensive collection of TypeScript interview questions and answers is your ultimate guide to mastering the skills you need for any TypeScript-based role.

Curated and answered by ex-FAANG interviewers with years of experience, our resource ensures you’re prepared for a variety of challenges. Whether you’re tackling algorithms, TypeScript functions, or building robust applications with strong typing, our questions are designed to reflect real-world scenarios. Each question is accompanied by detailed explanations, example solutions, and automated test cases, enabling you to refine your skills with immediate feedback.

Our resource is divided into two major categories: TypeScript Coding Interview Questions and TypeScript Quiz Interview Questions, covering a broad spectrum of topics essential for any TypeScript interview.

TypeScript Coding Interview Questions

Master critical TypeScript techniques and coding patterns with our curated list of TypeScript coding interview questions. These questions are designed to help you:

  1. Develop strongly typed data structures and algorithms: Solve challenges involving arrays, tuples, enums, interfaces, and generics, sharpening your problem-solving skills with TypeScript.
  2. Leverage TypeScript’s advanced features: Utilize utility types, mapped types, and conditional types to build modular and reusable functions and components.
  3. Enhance application safety: Use TypeScript’s type system to catch errors at compile-time and ensure code correctness.
  4. Handle real-world scenarios: Address challenges like API integrations, state management with typing, and designing scalable systems.

Each coding question includes:

  • Example solutions: Step-by-step implementations written in TypeScript to guide you through the problem-solving process.
  • Automated test cases: Instantly validate your solutions, ensuring accuracy and correctness.
  • Best practices: Learn coding techniques that prioritize readability, maintainability, and performance.

Our in-browser coding workspace allows you to practice directly in TypeScript with no setup required. You’ll gain hands-on experience with instant visual feedback, enhancing your understanding of TypeScript’s features.

Example coding questions you might encounter include:

  • How to implement a generic utility function to filter objects based on key-value pairs?
  • How to enforce type safety in a Redux store using TypeScript?
  • How to design a flexible API response handler using conditional types?

Each challenge mimics real-world tasks, equipping you with practical skills that go beyond theory.

TypeScript Quiz Interview Questions

TypeScript quiz questions test your understanding of the language’s fundamentals and intricacies. These trivia-style questions cover a wide range of topics, ensuring your readiness for interviews. Here’s what you’ll explore:

  1. Core TypeScript concepts: Understand key topics such as interfaces, type aliases, generics, and type inference.
  2. Advanced typing: Learn how to use conditional types, mapped types, and utility types to write concise and powerful code.
  3. Error handling: Explore techniques to handle runtime errors while maintaining type safety.
  4. Tooling: Familiarize yourself with TypeScript’s configuration options, including tsconfig.json, and its integration with build tools.
  5. Testing: Understand how to write type-safe tests using TypeScript with libraries like Jest and Mocha.

Each quiz question comes with:

  • Concise answers (TL;DR): Clear and to-the-point solutions to help you respond confidently during interviews.
  • Comprehensive explanations: In-depth insights to ensure you fully understand the concepts and can elaborate when required.

Example quiz topics include:

  • What is the difference between interface and type in TypeScript?
  • How does TypeScript’s unknown type differ from any?
  • How can you use mapped types to create a new type from an existing one?

These questions ensure that you’re not only familiar with TypeScript’s syntax but also understand how to apply its features effectively in various scenarios.

Why Choose Our TypeScript Interview Questions?

  1. Credibility: All questions and answers are crafted by ex-FAANG interviewers with deep expertise in assessing candidates and building TypeScript solutions for large-scale applications.
  2. Comprehensive Coverage: From algorithms and coding patterns to core concepts and advanced features, our resource spans every topic you need to master.
  3. Practical Focus: Each question reflects real-world challenges, helping you develop skills that are directly applicable to your career.
  4. Interactive Learning: Use our in-browser coding workspace to practice coding problems with instant feedback, simulating real interview conditions.

By leveraging this resource, you’ll develop skills that go beyond typical interview preparation. You’ll also gain confidence in tackling tasks like solving complex algorithms, debugging TypeScript code, and optimizing performance.

How These Questions Help You Excel

Our TypeScript interview questions are structured to help you:

  1. Master Core TypeScript Concepts: Strengthen your understanding of TypeScript’s syntax, features, and best practices.
  2. Develop Problem-Solving Skills: Learn to approach challenges systematically, breaking them down into manageable steps.
  3. Gain Hands-On Experience: Practice coding problems and see your solutions come to life in our interactive workspace.
  4. Communicate Effectively: Prepare to explain your thought process and solutions clearly, a crucial skill in technical interviews.

Real-World Applications

The scenarios covered in this resource aren’t just theoretical. They reflect the types of challenges developers face daily, such as:

  • Designing type-safe APIs and SDKs for scalable systems.
  • Writing reusable and maintainable TypeScript functions and components.
  • Debugging and optimizing code for performance and type safety.

By mastering these areas, you’ll not only be interview-ready but also prepared to excel on the job, making you a standout candidate for any TypeScript-related role.