Step 3 / Select topic TypeScript Hard

What this bank covers

• Distributive conditional with infer
• Excess property checks need a fresh literal
• const assertions on array literals
• Inference through keyof and indexed access
• unknown is not assignable downward
• keyof with a string index signature
• Template literal inference over a union
• Distribution happens before the array wrap
• Tuple inference from rest parameters
• satisfies and literal widening
• typeof "object" keeps null in the union
• Fall-through cases narrow to a sub-union
• Truthiness checks also exclude 0
• User-defined type guards narrow both branches
• Array.isArray narrows a union element
• Exhaustiveness checks need every member handled
• Boolean literals work as discriminants
• typeof "function" narrows callable union members
• instanceof narrowing with a subclass
• Truthiness narrowing discards falsy members
• Interface declaration merging
• An interface can extend an object type alias
• implements requires statically known members
• Type aliases do not merge
• extends checks member compatibility
• keyof over a merged interface
• Intersections combine conflicting members as never
• Implicit index signatures: alias yes, interface no
• Call signatures vs function type aliases
• Intersecting an optional member with a required one
• Generic pick and duplicate keys
• Distributive conditional types with infer
• Constrained generic over a record of numbers
• One type parameter, two conflicting inference sites
• Recursive generic tuple building
• Variadic infer in tuple patterns
• Distribution over the never type
• Key remapping in a generic mapped type
• Indexed access types link key and value
• Method bivariance in generic interfaces
• Exclude over keyof unions
• ReturnType with overloads
• Parameters with optional and rest parameters
• Key remapping with Capitalize
• Awaited unwraps recursively
• Omit over a union type
• Readonly is shallow
• ReturnType of an uninstantiated generic signature
• NonNullable over a union
• Which arguments still carry a literal type
• Template literal types distribute over unions
• Key remapping keeps the original literal available
• Numeric keys yield numeric literal types
• Widening inside mutable object literals
• Literal inference from a string constraint
• Template literal types distribute and are case-sensitive
• Assignability between literal unions and related types
• Literal discriminants drive narrowing
• as const tuples as a source of key literal types
• Distributive conditional types and never
• unknown as the top type
• keyof any
• unknown is not assignable to anything but unknown and any
• never as an exhaustiveness check
• Assignability among any, unknown and never
• any, unknown and never in intersections
• unknown in unions
• any in conditional types
• any disables property checking
• Field initialization order with inheritance
• Static property initialization order
• Private-field brand checks
• Abstract classes and constructor types
• Class expressions as mixins
• Arrow-function fields and dynamic dispatch
• Accessors versus instance fields in serialization
• Derived field initializers run after super()
• Static blocks interleave with static fields
• Reverse mapping after an explicit initializer
• String enums have no reverse mapping
• Key count of a numeric enum object
• Enum nominality for string enums
• Constant enum expressions in a const enum
• as const produces a readonly tuple
• const assertions are erased at runtime
• Merged enum declarations and key ordering
• Duplicate enum values collide in the reverse map
• Merging a namespace into an enum
• Non-null assertion is erased
• Casts do not convert values
• Abstract classes survive erasure
• Overload signatures are compile-time only
• Optional parameters are not filled in
• Predicates are trusted, not verified
• readonly is checked, not enforced
• private vs #private at runtime
• satisfies has no runtime effect
• Optional properties are not created
• Field initialization order vs. overridden methods