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TypeScript Academy · Lesson

Template Literal Types: String Patterns

Combine string unions into pattern types.

Lesson 3 of 413 steps

Template Literal Types: String Patterns is a free TypeScript Academy lesson on CoddyKit. This is lesson 3 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the TypeScript Academy learning path, and your progress syncs across the web and the CoddyKit app. The TypeScript Academy course includes 4 lessons in total.

Welcome

Template literal types use backtick syntax at the type level to construct string types from combinations of other string types.

Basic Template Literal Type

Combine string literal types with template syntax.
type Greeting = `Hello, ${string}`;
const g: Greeting = 'Hello, World'; // OK
// const bad: Greeting = 'Hi there'; // Error

Combining Unions

When a union is used in a template literal, TypeScript generates all combinations.
type Color = 'red' | 'green' | 'blue';
type Size = 'sm' | 'lg';
type ColorSize = `${Color}-${Size}`;
// 'red-sm' | 'red-lg' | 'green-sm' | ...

Event Names Pattern

A common use: generating typed event names from entities.
type Entity = 'user' | 'product';
type EventName = `on${Capitalize<Entity>}Created`;
// 'onUserCreated' | 'onProductCreated'

Capitalize and Other Intrinsic Types

TypeScript provides Capitalize, Uncapitalize, Uppercase, Lowercase as built-in string manipulation types.
type T = Capitalize<'hello world'>; // 'Hello world'
type U = Uppercase<'hello'>;        // 'HELLO'
type L = Lowercase<'WORLD'>;        // 'world'

Getter Generation Pattern

Use template literal types with mapped types to generate getter method names.
type Getters<T> = {
  [K in keyof T as `get${Capitalize<string & K>}`]: () => T[K]
};

Typed Route Parameters

Extract typed route parameters from a URL pattern string.
type RouteParams<T extends string> =
  T extends `${infer _Start}:${infer Param}/${infer Rest}`
    ? Param | RouteParams<Rest>
    : T extends `${infer _Start}:${infer Param}`
    ? Param
    : never;

CSS Property Naming

Generate typed CSS custom property names.
type CSSVar = `--${string}`;
const color: CSSVar = '--primary-color'; // OK

Template Literal in Function Parameters

Use template literal types to constrain string parameters.
function emit<E extends `on${string}`>(event: E): void {
  console.log('Emitting:', event);
}
emit('onClick'); // OK
// emit('click'); // Error — must start with 'on'

Extracting Parts with infer

Use infer inside template literals to extract sub-strings at the type level.
type GetSuffix<T extends string> =
  T extends `${infer _Prefix}_${infer Suffix}` ? Suffix : never;
type S = GetSuffix<'user_created'>; // 'created'

Intersection with Record

Combine template literal types with Record for typed event handler maps.
type Handlers<T extends string> = Record<`on${Capitalize<T>}`, () => void>;

Quick Check

What does `type R = `${string | number}-id`` evaluate to?
Answer it in the interactive lesson

Recap

Template literal types construct string types from combinations using backtick syntax. They distribute over unions, work with Capitalize/Uppercase helpers, and enable powerful patterns for event names, route params, and CSS variables.
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Frequently Asked Questions

Is the “Template Literal Types: String Patterns” lesson free?

Yes — the full text of “Template Literal Types: String Patterns” is free to read here on the web. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the TypeScript Academy course, upgrade to CoddyKit PRO. The TypeScript Academy course includes 4 lessons in total.

What will I learn in “Template Literal Types: String Patterns”?

Combine string unions into pattern types. You practise TypeScript Academy with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.

Do I need any experience to start TypeScript Academy?

No prior experience is required. TypeScript Academy on CoddyKit is structured for beginners through advanced learners, so you can start here or from the beginning and move at your own pace. This is lesson 3 of 4.

How long does the “Template Literal Types: String Patterns” lesson take?

Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.

Can I write and run code in this TypeScript Academy lesson?

Yes. Every TypeScript Academy lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.

All lessons in this course

  1. Mapped Types: Transforming Object Types
  2. Modifiers in Mapped Types: readonly and ?
  3. Template Literal Types: String Patterns
  4. Key Remapping with as in Mapped Types
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