The Work Gym

Courses / Programming

JavaScript and TypeScript

Write JavaScript, check strict TypeScript, and build libraries that survive hidden tests.

Start lesson 1 Practice interview Take the assessmentPractice the first unit of every course. No account needed.

61lessons

334checked exercises

14projects, cases and exams

Prepares you for JavaScript and TypeScript engineering interviews

Projects, case studies and mock exams

Project · IntermediateTyped API client

Cedar Scheduling, a fictional appointment planner, needs a client for a local mocked person endpoint.

7 steps Case study · IntermediateBlocked work review

Juniper Media, a fictional production desk, must choose which team to review first.

5 steps Project · AdvancedTyped event delivery

Practice typed event emitter in original workplace code.

8 steps Project · AdvancedRetrying task queue

Practice retry budgets and deterministic scheduling in original workplace code.

8 steps Project · AdvancedForm validation library

Practice composable form validation in original workplace code.

8 steps Case study · AdvancedSettlement release

Practice typed payment reconciliation in original workplace code.

5 steps Mock exam · AdvancedAdvanced language assessment

Practice timed advanced implementation assessment in original workplace code.

8 questions · 45 min Project · ExpertTyped transformation pipeline

Practice validated transformation pipelines in original workplace code.

8 steps Case study · ExpertImport failure investigation

Practice evidence-based failure diagnosis in original workplace code.

5 steps Mock exam · ExpertExpert language assessment

Practice timed expert language assessment in original workplace code.

8 questions · 50 min

Start with JavaScript values, functions and collections, then learn async work and the TypeScript type system. You write real functions in the code editor and run them against visible examples and hidden boundary cases. TypeScript tasks check compiler diagnostics as well as runtime results.

Build a typed API client, an event emitter with a retry queue, a validation library and a transformation pipeline. Practice interviews and timed job tests cover frontend, backend and library work. Mock APIs, modules and file operations use supplied local fixtures in your browser. This workspace teaches a supported subset of Node APIs; it doesn't connect to a server or open your computer's files.

Beginner

JavaScript foundations

Read values, make explicit conversions, and trace branches and bindings.

5 lessons

1Values and typesJavaScript values have types even when a variable has no annotation.6 exercisesFree

2Coercion and equalityA form field usually arrives as text.4 exercisesFree

3Branches and loopsA branch turns a rule into a choice.4 exercisesFree

4Scope and hoistingA binding belongs to a scope.4 exercisesFree

Practice setFoundations practiceYou are reviewing small utility functions for Lumen Dispatch, a fictional delivery planner.Free

Collections and records

Transform arrays and objects while preserving order, identity, and empty values.

5 lessons

6Array operationsAn array keeps an ordered sequence of values.4 exercisesWith a plan

7Objects and destructuringObject properties describe named fields.4 exercisesWith a plan

8Higher-order functionsA higher-order function accepts a function or returns one.4 exercisesWith a plan

9Map, Set, and WeakMapSet stores distinct values in first-insertion order.4 exercisesWith a plan

Practice setCollections practiceHarbor Studio, a fictional production team, needs collection utilities for its planning board.With a plan

Functions and object behavior

Trace private state, receivers, prototypes, and validated text boundaries.

6 lessons

11Closures and private stateA closure is a function together with the lexical environment it can access.4 exercisesWith a plan

12Receivers and thisFor an ordinary function, this depends on how the function is called.4 exercisesWith a plan

13Prototypes and classesAn object can inherit fields and methods from a prototype.4 exercisesWith a plan

14JSON and regular expressionsText at a data boundary needs both parsing and validation.4 exercisesWith a plan

Interview setEasy JavaScript interview setExplain small language contracts, implement them, and defend their boundary cases.With a plan

Practice setBehavior practiceMoss Travel, a fictional scheduling service, is reviewing small functions that keep state and read external text.With a plan

Intermediate

Async work and iteration

Trace Promise outcomes and queued jobs, then consume lazy and asynchronous sequences.

5 lessons

17Promises and outcomesA Promise represents an eventual outcome.4 exercisesWith a plan

18Async control and errorsAn async function can suspend at await and resume after the awaited Promise settles.4 exercisesWith a plan

19Jobs and execution orderJavaScript completes the current synchronous work before running queued Promise reactions.4 exercisesWith a plan

20Iterators and generatorsAn iterator returns a sequence through next calls, each with a value and a done flag.4 exercisesWith a plan

Practice setAsync and iteration practiceFern Logistics, a fictional dispatch service, needs utilities that preserve execution order while handling failed work.With a plan

TypeScript foundations

Use narrowing, object contracts, and generics to preserve relationships in reusable helpers.

5 lessons

22Types and inferenceTypeScript checks relationships before the program runs.4 exercisesWith a plan

23Narrowing and type guardsA union describes several possible shapes.4 exercisesWith a plan

24Interfaces and type aliasesAn interface describes an object contract.4 exercisesWith a plan

25Generics and constraintsA generic type parameter preserves a relationship across a function's inputs and outputs.4 exercisesWith a plan

Practice setTyped foundations practiceAlder Payments, a fictional internal tools team, is replacing loosely checked utility functions with explicit contracts.With a plan

Typed application boundaries

Build a validated local API client and support a queue recommendation with checked evidence.

5 lessons

27Dates and IntlA Date represents a timestamp, while a calendar date depends on a time zone.4 exercisesWith a plan

28Local Node conceptsNode programs commonly split code into modules, read files, process chunks, and run assertions.4 exercisesWith a plan

ProjectTyped API clientCedar Scheduling, a fictional appointment planner, needs a client for a local mocked person endpoint.With a plan

Case studyBlocked work reviewJuniper Media, a fictional production desk, must choose which team to review first.With a plan

Practice setIntegration practiceBirch Retail, a fictional operations team, is combining small utilities into a local reporting workflow.With a plan

Advanced

Reusable type contracts

Build generic APIs and derive precise types for related records.

5 lessons

32Generic collection contractsPractice generics and constraints in original workplace code.4 exercisesWith a plan

33Utility types for public APIsPractice partial pick omit required and readonly in original workplace code.4 exercisesWith a plan

34Mapped types and key remappingPractice mapped types and modifiers in original workplace code.4 exercisesWith a plan

35Conditional and template literal typesPractice conditional types template literals and enum alternatives in original workplace code.4 exercisesWith a plan

Practice setType API practicePractice mixed generic api contracts in original workplace code.With a plan

Typed application services

Build event delivery, retries, validation, and strict adapters.

5 lessons

40Declarations and strict boundariesPractice declaration contracts unknown and strict mode in original workplace code.4 exercisesWith a plan

ProjectTyped event deliveryPractice typed event emitter in original workplace code.With a plan

ProjectRetrying task queuePractice retry budgets and deterministic scheduling in original workplace code.With a plan

ProjectForm validation libraryPractice composable form validation in original workplace code.With a plan

Practice setService contract practicePractice mixed service reliability contracts in original workplace code.With a plan

Concurrent work and assessment

Coordinate promises, reconcile payments, and solve assessed tasks.

5 lessons

42Promise coordination contractsPractice promise aggregation and cleanup in original workplace code.4 exercisesWith a plan

Case studySettlement releasePractice typed payment reconciliation in original workplace code.With a plan

Interview setMedium implementation interviewPractice medium typed implementation questions in original workplace code.With a plan

Mock examAdvanced language assessmentPractice timed advanced implementation assessment in original workplace code.With a plan

Practice setAdvanced review practicePractice mixed advanced language review in original workplace code.With a plan

Expert

Identity, timing, and state

Control object graphs, structural equality, scheduled work, and state transitions.

5 lessons

47Deep clone and object graphsPractice deep clone identity and cycles in original workplace code.4 exercisesWith a plan

48Structural equality contractsPractice deep equality and special values in original workplace code.4 exercisesWith a plan

49Debounce and throttlePractice debounce throttle cancellation and fake clocks in original workplace code.4 exercisesWith a plan

50Typed state machinesPractice discriminated events and guarded transitions in original workplace code.4 exercisesWith a plan

Practice setRuntime correctness practicePractice mixed identity timing and state contracts in original workplace code.With a plan

Typed pipelines and reusable helpers

Build a reconciled pipeline with functional, type, and iterable contracts.

5 lessons

53Functional API contractsPractice currying composition result mapping and memoization in original workplace code.4 exercisesWith a plan

54Advanced type relationshipsPractice recursive conditional types union extraction and route types in original workplace code.4 exercisesWith a plan

55Streams and iterable transformsPractice chunk framing generators and async iteration in original workplace code.4 exercisesWith a plan

ProjectTyped transformation pipelinePractice validated transformation pipelines in original workplace code.With a plan

Practice setPipeline and type reviewPractice mixed functional and stream contracts in original workplace code.With a plan

Investigation and software interviews

Diagnose failures and solve runtime, implementation, and timed assessments.

5 lessons

Case studyImport failure investigationPractice evidence-based failure diagnosis in original workplace code.With a plan

Interview setRuntime output interviewPractice event loop this binding and closure prediction in original workplace code.With a plan

Interview setHard implementation interviewPractice hard reusable language utilities in original workplace code.With a plan

Mock examExpert language assessmentPractice timed expert language assessment in original workplace code.With a plan

Practice setExpert review practicePractice mixed expert language review in original workplace code.With a plan