019 min
Why types exist
Catch bad assumptions early
MINI BUILDCreate typed variables for customerName, orderTotal and isPaid using string, number and boolean.
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🔷 TYPE SAFETY LAB
TypeScript, taught through useful outcomes.
Learn JavaScript with guardrails: describe the shape of your data so mistakes surface before users find them.
14 guided lessons≈ 170 guided minutesLearn → Try → Test → Build✓ Full journey + boss live
GUIDED ROADMAP
One concept at a time. One useful build each time.
Lessons unlock in order so the next step stays obvious. Completed lessons remain available for review, and the boss project unlocks only after the full journey.
YOUR GUIDED JOURNEYRestoring saved progress…
029 min
Primitive types
Describe basic values
MINI BUILDType a small customer summary with name, age, totalSpend and subscribed fields.
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0311 min
Arrays & objects
Describe real data
MINI BUILDCreate a typed array of three courses containing title and minutes for each item.
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0411 min
Typed functions
Type inputs and outputs
MINI BUILDWrite a typed discount function that accepts price and percent as numbers and returns a number.
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0512 min
Type aliases & interfaces
Name reusable shapes
MINI BUILDDefine an interface called Course with id, title, minutes and completed, then type two variables with it.
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0612 min
Interfaces & extension
Compose domain contracts without duplication
MINI BUILDDefine a BaseRecord interface and extend it into a ProductRecord with price and stock.
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0712 min
Unions
Represent valid alternatives
MINI BUILDCreate a LessonStatus union with locked, current and complete, then type a variable with it.
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0813 min
Narrowing
Prove what a value is
MINI BUILDWrite a function that accepts string | number and returns a readable label after narrowing with typeof.
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0912 min
Optional & readonly fields
Model what may be absent and what must not change
MINI BUILDType an Order with readonly id, required total and optional customerNote.
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1015 min
Generics
Reuse types without losing meaning
MINI BUILDCreate a Box<T> type with a value field, then make one Box<string> and one Box<number>.
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1113 min
Utility types
Derive useful views of existing contracts
MINI BUILDCreate ProductSummary with Pick and ProductPatch with Partial/Omit from one Product interface.
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1214 min
Typing async results
Model success and failure at asynchronous boundaries
MINI BUILDWrite a typed async function returning Promise<number> and include a clear failure path.
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1314 min
React-oriented type mental models
Understand props and event boundaries without framework magic
MINI BUILDDefine a TaskRowProps type with title, completed and an optional onToggle callback.
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1413 min
Debugging compiler errors
Read type failures as failed assumptions
MINI BUILDCreate a small typed function, write one intentionally invalid call, and explain the compiler complaint in plain language.
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FINAL BOSS
Checking your lesson progress…Typed Order Feature Boss
Design a small feature whose data contracts make invalid states harder to express.
JOURNEY + BOSS LIVE
TypeScript has a complete guided arc.
The journey includes 14 sequenced lessons, local mastery and a final project that checks whether the major ideas were combined.
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