01
CheckingnewbieBuild a utility
Introduce a Learner
Return a friendly greeting from a learner's display name.
Values and strings
- values
- strings
- functions
10 minStart
JavaScript learning path
Build JavaScript skill from fundamentals to interview practice.
Work through focused modules covering data, functions, async behavior, browser runtime, and real interview trade-offs. Start anywhere, then use the suggested order to build stronger evidence.
35
Available activities
6
Learning modules
Newbie to hard
Progression within modules
Modules group related concepts. Activities move from easy to hard; prerequisites guide you without blocking experienced learners.
Module 0
JavaScript basics
Start with plain JavaScript: values, decisions, loops, strings, arrays, and small functions.
15 activitiesChecking progress
ValuesConditionalsLoopsStringsArraysmap and filterFunctionsSpreadGetters and setters
02
CheckingnewbieBuild a utility
Classify a Number
Decide whether a number is positive, negative, or zero.
Conditionals
- numbers
- conditionals
- comparison
10 minStart
03
CheckingnewbieBuild a utility
Count Even Values
Count how many values in a list can be divided by two without a remainder.
Loops and numbers
- arrays
- loops
- numbers
12 minStart
04
CheckingnewbieBuild a utility
Sum the Values
Add every number in a list and return the total.
Loops and arrays
- arrays
- loops
- accumulation
12 minStart
05
CheckingnewbieBuild a utility
Find the Largest Value
Return the largest number in a list, or null when the list is empty.
Arrays and comparisons
- arrays
- loops
- comparisons
15 minStart
06
CheckingnewbieBuild a utility
Reverse a Word
Return the characters of a word in reverse order.
Strings
- strings
- loops
12 minStart
07
CheckingnewbieBuild a utility
Count Vowels
Count the vowels in a word without treating uppercase and lowercase differently.
Strings and conditions
- strings
- loops
- conditionals
15 minStart
08
CheckingnewbieBuild a utility
Repeat a Message
Return a list containing the same message a requested number of times.
Loops and arrays
- loops
- arrays
- functions
12 minStart
09
CheckingnewbieBuild a utility
Calculate an Average
Return the average of a list of scores, or null when no scores exist.
Arrays and arithmetic
- arrays
- loops
- arithmetic
15 minStart
10
CheckingnewbieBuild a utility
Capitalize Words
Return a sentence with the first letter of every word uppercase.
Strings and arrays
- strings
- arrays
- loops
15 minStart
11
CheckingnewbieBuild a utility
Map Score Labels
Use map to turn numeric scores into readable labels without changing the original list.
map and arrays
- arrays
- map
- functions
15 minStart
12
CheckingnewbieBuild a utility
Build a Study Label
Use an implicit return in a small helper and an explicit return in the main function.
Explicit and implicit returns
- functions
- arrow functions
- strings
15 minStart
13
CheckingnewbieBuild a utility
Merge Preferences with Spread
Create a new preferences object by combining defaults with user overrides.
Spread operator
- objects
- spread
- immutability
15 minStart
14
CheckingnewbieBuild a utility
Clamp Progress with a Setter
Use a setter to keep a progress value between zero and one hundred.
Getters and setters
- objects
- setters
- getters
18 minStart
15
CheckingnewbieBuild a utility
Filter Passing Scores
Keep only scores that meet the practice passing mark.
filter and arrays
- arrays
- filter
- conditionals
15 minStart
Module 1
Working with data
Build reliable instincts for values, objects, arrays, and safe transformations.
9 activitiesChecking progress
TypesArraysObjectsDestructuringImmutability
01
CheckingeasyBuild a utility
Request Label Normalizer
Build predictable display labels from mixed request records without mutating the source list.
Arrays and objects
- arrays
- objects
- immutability
25 minStart
02
CheckingeasyDebug and repair
Release-Order Comparator
Repair a release ordering helper so it is deterministic and leaves the input untouched.
Sorting and runtime types
- sorting
- comparator
- mutation
30 minStart
03
CheckingeasyDebug and repair
Filter-State Snapshot
Repair a nested state update that accidentally changes a previous snapshot.
References and immutability
- references
- objects
- immutability
25 minStart
04
CheckingeasyBuild a utility
Computed Field Updater
Update a named deployment field without mutating the existing form object.
Object updates
- objects
- computed properties
- immutability
25 minStart
05
CheckingeasyBuild a utility
Optional Config Reader
Read a safe retry delay from incomplete client configuration.
Optional data and defaults
- optional chaining
- runtime types
- configuration
25 minStart
06
CheckingmediumBuild a utility
Safe Response Boundary
Turn unknown release API data into safe row records without assuming its shape.
Runtime types and guards
- runtime types
- nullability
- validation
35 minStart
07
CheckingmediumBuild a utility
Destructured Release Summary
Read nested release data with defaults and return a stable summary.
Destructuring
- destructuring
- defaults
- objects
30 minStart
08
CheckingmediumBuild a utility
Safe JSON Preferences
Parse stored preferences without letting invalid storage break the UI.
Parsing and error handling
- json
- errors
- storage
35 minStart
09
CheckingmediumBuild a utility
Request Result Classifier
Convert unknown request outcomes into a small UI-safe result contract.
Error boundaries
- errors
- runtime types
- api data
35 minStart
Module 2
Functions and execution
Understand the execution model behind closures, callbacks, receivers, and modules.
6 activitiesChecking progress
ScopeClosuresHigher-order functionsthisPrototypesModules
01
CheckingeasyBuild a utility
Scoped Notification Counter
Use a closure to keep independent notification counts private to each counter.
Closures and scope
- closures
- scope
- functions
35 minStart
02
CheckingeasyDebug and repair
Callback Context Repair
Repair an extracted method that loses the release object it should describe.
this and callbacks
- this
- callbacks
- bind
35 minStart
03
CheckingmediumBuild a utility
Release Check Pipeline
Apply a sequence of named checks by treating functions as values.
Higher-order functions
- functions
- higher order functions
- pipelines
30 minStart
04
CheckingmediumTrace and explain
Prototype Owner Report
Distinguish instance data from shared prototype behavior.
Prototype delegation
- prototypes
- constructors
- objects
35 minStart
05
CheckingmediumBuild a utility
Private Preference Module
Keep a preference value private behind a small closure-based API.
Closures and modules
- closures
- module pattern
- privacy
35 minStart
06
CheckingmediumBuild a utility
Feature Module Contract
Expose a narrow feature-flag module instead of leaking mutable internal state.
Module boundaries
- modules
- closures
- api design
40 minStart
Module 3
Asynchronous JavaScript
Reason about ordering, failure, cancellation, and competing asynchronous work.
5 activitiesChecking progress
Event loopPromisesasync/awaitRetriesTimersCancellation
01
CheckingeasyTrace and explain
UI Task Ordering
Predict and implement the observable order of synchronous work, promise callbacks, and timers.
Event loop ordering
- event loop
- promises
- timers
40 minStart
02
CheckingeasyBuild a utility
Retryable Preference Save
Retry a transient preference-save failure and return a predictable result.
Promises and retries
- promises
- async
- errors
45 minStart
03
CheckingmediumDebug and repair
Search Request Coordinator
Prevent an older search response from replacing the newest query result.
Stale requests and recovery
- async
- promises
- stale results
45 minStart
04
CheckingmediumBuild a utility
Debounced Query Settler
Model the final query that remains after rapid input changes settle.
Timers and cancellation
- debounce
- timers
- closures
40 minStart
05
CheckinghardBuild a utility
Request Timeout Race
Return a timeout result when a simulated request cannot finish in budget.
Races and time budgets
- promises
- timeout
- async
45 minStart
Module 4
Browser runtime
Apply JavaScript knowledge to DOM events, browser APIs, and real UI boundaries.
Coming next
DOMEventsDelegationStorageNetworkCleanup
This module is planned. New activities will appear here as they pass the content and test quality review.
Module 5
Interview synthesis
Combine multiple concepts while debugging, reviewing, refactoring, and explaining code.
Coming next
DebuggingCode reviewRefactoringTrade-offsTimed practice
This module is planned. New activities will appear here as they pass the content and test quality review.