Pattern matching with template literals in Typescript - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is pattern matching with template literals in TypeScript?

It is a way to check if a string fits a specific pattern using template literal types, allowing you to extract parts of the string or validate its format at compile time.

intermediate

How do you extract parts of a string using template literal pattern matching?

You use the infer keyword inside a conditional type with template literals to capture parts of the string into type variables.

intermediate

Example: What does this type do?<br>

type ExtractName<T> = T extends `Hello, ${infer Name}!` ? Name : never;

It extracts the Name part from strings that start with 'Hello, ' and end with '!'. For example, ExtractName<'Hello, Alice!'> = 'Alice'.

advanced

Can template literal pattern matching check for exact string formats at compile time?

Yes, TypeScript can use template literal types in conditional types to verify if a string matches a pattern and produce different types based on that.

beginner

What happens if a string does not match the pattern in a template literal conditional type?

The conditional type returns the 'false' branch, often never or another fallback type, indicating no match.

Which keyword is used to capture parts of a string in template literal pattern matching?

A match

B extract

C capture

D infer

The infer keyword is used inside conditional types to capture parts of a string matched by template literals.

What will ExtractName<'Hello, Bob!'> return if type ExtractName<T> = T extends `Hello, ${infer Name}!` ? Name : never;?

A never

B 'Bob'

C 'Hello, Bob!'

D string

The type extracts 'Bob' from the string because it matches the pattern.

If a string does not match the pattern in a conditional template literal type, what is the result?

A never

B string

C undefined

D any

The conditional type returns the false branch, often never, indicating no match.

Can template literal pattern matching be used to validate string formats at compile time?

A Only at runtime

B No

C Yes

D Only with regular expressions

TypeScript can check string formats at compile time using template literal types and conditional types.

Which of these is a valid pattern for matching a string starting with 'ID-' followed by any characters?

A `ID-${string}`

B `${string}ID-`

C `ID-${number}`

D `${number}-ID`

The pattern `ID-${string}` matches strings starting with 'ID-' followed by any string.

Explain how template literal pattern matching works in TypeScript and how you can extract parts of a string.

Think about how you can capture parts of a string inside a type.

Describe a use case where pattern matching with template literals can help in TypeScript programming.

Consider how you might check or extract parts of strings without running code.