JavaScript Array Exercises
Master JavaScript arrays with interactive exercises covering indexes, length, mutation, copying, iteration, chunking, deduplication, zipping, merging, intersections, flattening, and array algorithms. Write and test real code in your browser with immediate feedback.
Exercises
Work from beginner to very hard, or use the filters to find a specific skill.
Array Index Reassignment
Array indexes read and write positions in an ordered list. When you assign to an...
Array Length
The `.length` property tells you how many items are currently in an array. Becau...
Push Return Value
`push` changes an array by adding an item to the end. Its return value is the ne...
Slice Range Copy
`slice` copies part of an array into a new array. The start index is included, a...
Safe Array Indexing
Array indexing returns `undefined` when a position does not exist. That can be f...
Append Without Mutation
Some array methods change the existing array, while other patterns create a sepa...
Replace Without Mutation
Replacing an array item by index is direct, but doing it on the input array chan...
Insert Into a Copy
Practice JavaScript array insertion by placing a value at a requested position i...
Remove One Matching Value
Practice JavaScript array removal by deleting only the first matching value from...
Array Type Check
Arrays are objects in JavaScript, so a broad object check cannot tell you whethe...
Chunking Arrays
Practice JavaScript array chunking by turning one list into fixed-size groups. T...
Array Rotation
Practice JavaScript array rotation by moving leading items to the end in a copie...
Deduping Without Reordering
Practice JavaScript array deduping by keeping the first occurrence of each value...
Removing a Range
Practice JavaScript array range removal by copying everything around a deleted s...
Zipping Arrays
Practice JavaScript array zipping by pairing values from two lists into nested a...
Fill Sparse Slots
Practice filling sparse JavaScript arrays by replacing missing slots without con...
Sorted Array Merge
Practice JavaScript sorted array merging by combining two already ordered number...
Moving an Array Item
Practice JavaScript array reordering by moving one item between indexes in a cop...
Sliding Window Totals
Calculate JavaScript array window totals for overlapping consecutive groups. Thi...
Consecutive Run Compression
Practice JavaScript array traversal by compressing consecutive repeated values i...
Array Intersection
Practice JavaScript array intersection by returning the unique values shared by ...
Merging Overlapping Ranges
Practice JavaScript arrays with interval merging by sorting copied range pairs b...
Applying a List Patch
Practice JavaScript array updates by applying ordered insert, remove, and replac...
Deep Flatten
Practice recursive JavaScript array flattening by walking nested lists at any de...
Cartesian Product
Practice JavaScript cartesian products by pairing every value from one array wit...
Async Sequence
Practice sequential async JavaScript over an array of task functions. This resto...
Practice JavaScript arrays as ordered data
Arrays store ordered collections and appear throughout JavaScript in lists, queues, search results, application state, and API data. These JavaScript array exercises help you read, update, copy, iterate through, reshape, and compare collections while keeping order and mutation behavior clear.
The collection starts with index reassignment, array length, the return value of push, range copies with slice, safe indexing, type checks, and non-mutating append, replace, insert, and removal patterns. This JavaScript array methods practice focuses on what each operation returns and whether it changes the original array.
The array iteration practice problems then develop into chunking, rotation, deduplication, zipping, sparse slots, sorted merges, sliding windows, run compression, intersections, overlapping ranges, list patches, deep flattening, Cartesian products, and sequential async work. These are real array-processing decisions rather than repetitions of isolated method names.
- Exercises
- 26
- Difficulty
- Beginner to Very Hard
- Good to know first
- Know how to declare variables, read a small function, and follow a basic loop before attempting the harder array algorithms.
What you’ll practice
- Read and update array values safely by index
- Understand array length and method return values
- Copy, append, replace, insert, and remove without mutation
- Iterate through arrays while preserving order
- Chunk, rotate, zip, deduplicate, and fill collections
- Merge sorted data and calculate sliding-window totals
- Find intersections and combine overlapping ranges
- Flatten nested arrays and build advanced array transformations
Who these exercises are for
This practice set begins with approachable array fundamentals and progresses to harder collection algorithms. It suits learners strengthening core JavaScript, students looking for array iteration practice problems, and developers who want to reason more carefully about mutation, order, and result shapes.
How practice works
- Write and run JavaScript directly in your browser
- Use instant test feedback to catch indexing and mutation mistakes
- Progress from basic array operations to multi-step algorithms
- Filter exercises by difficulty and save your progress when signed in