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Aporeon

Technical interview practice, from one developer to another.

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Frontend Engineering Foundations

TypeScript Type System

Structural typing, generics, contracts, nullability, checking tools, and maintainable type derivation.

6 drillsPractice one at a timeOrdered pathConcept questionComparison questionDebugging scenarioArchitecture scenario

Recommended start

Structural typing

Explains assignability by shape, excess-property checks, and the gap between compile-time compatibility and runtime identity.

Easy~5 minStep 1 of 6

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1Structural typingRecommended startExplains assignability by shape, excess-property checks, and the gap between compile-time compatibility and runtime identity.Concept questionEasy~5 minJavaScriptTypeScriptPractice 2Generics and constraintsUses generics to preserve relationships between types and constraints to express the operations an implementation requires.Concept questionMedium~7 minJavaScriptTypeScriptPractice 3Interface vs type aliasChooses interfaces or aliases based on object contracts, unions, composition, declaration merging, and team consistency.Comparison questionMedium~7 minJavaScriptTypeScriptPractice 4Nullability and optional dataSeparates optional, undefined, null, and invalid external data, then narrows values at the correct boundary.Debugging scenarioMedium~10 minJavaScriptTypeScriptPractice 5Annotation, assertion, or satisfiesSeparates declared variable types, unchecked developer assertions, and compatibility checking that preserves useful inferred types.Comparison questionMedium~7 minJavaScriptTypeScriptPractice 6Utility and mapped typesUses derived types for genuine relationships while preserving explicit boundaries for domain and transport models.Architecture scenarioMedium~10 minJavaScriptTypeScriptPractice

Practice order

6 drillsOne at a time

1Structural typingUp next / Easy / ~5 min
2Generics and constraintsMedium / ~7 min
3Interface vs type aliasMedium / ~7 min
4Nullability and optional dataMedium / ~10 min
5Annotation, assertion, or satisfiesMedium / ~7 min
6Utility and mapped typesMedium / ~10 min