JAVASCRIPT PRACTICE
Build stronger JavaScript instincts.
Work through focused JavaScript exercises from approachable foundations to more demanding problem-solving patterns.
11JavaScript exercises
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JavaScript EXERCISES
Each level includes test feedback and a solution.js reference tab.Choose your level
beginner
4 exercisesBeginner · build the foundation
Start with one core idea at a time and make the basic moves feel automatic.
01020304
JavaScriptbeginner
Group orders by status
Return an object whose keys are order statuses and whose values preserve the matching orders in their original order.
JavaScriptbeginner
Mask an email address for display
Return a privacy-friendly display value for a valid email: retain the first local-part character, replace the remaining local characters with asterisks, and keep the domain unchanged. Return null for malformed input.
JavaScriptbeginner
Normalize a list of tags
Return a new list of lower-case, trimmed tags with empty values removed and duplicates discarded while preserving first-seen order.
JavaScriptbeginner
Reverse the words
Return the words in a sentence in reverse order without reversing each word.
intermediate
4 exercisesIntermediate · connect the pieces
Combine concepts, validate inputs, and make practical design decisions.
01020304
JavaScriptintermediate
Build a safe query string
Convert a filter object into a query string, omitting null, undefined, empty strings, and false values while keeping zero.
JavaScriptintermediate
Calculate a cart total in cents
Return the total price in cents for cart lines. Ignore non-positive quantities and avoid floating-point money calculations.
JavaScriptintermediate
Group transactions
Group transactions by category and calculate an exact total for every category.
advanced
3 exercisesAdvanced · handle real-world constraints
Work with edge cases, maintainability, and the tradeoffs found in production code.
010203
JavaScriptadvanced
Detect conflicting calendar slots
Return true when a proposed time slot overlaps an existing slot. Time ranges use half-open intervals: an event ending at 10:00 does not conflict with one starting at 10:00.
JavaScriptadvanced
Limit concurrent async tasks
Implement a scheduler that starts at most limit promise-returning tasks at a time and resolves results in input order.
JavaScriptadvanced
Model async request states
Implement a reducer for idle, loading, success, and error request states. Ignore stale response actions whose requestId does not match the active request.
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