TypeScript. Lessons for beginners

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TypeScript 5.x Updates

TypeScript is actively maintained and updated by Microsoft. In version 5.x a lot of utility and quality of life updates were made.

This chapter covers the most popular updates to allow stricter and more flexible type safety.

As a reminder, these features will only be available in 5.x+

Template Literal Types

Template Literal Types now allows us to create more precise types using template literals. We can define custom types that depend on the actual values of strings at compile time.


type Color = "red" | "green" | "blue";
type HexColor<T extends Color> = `#${string}`;

// Usage:
let myColor: HexColor<"blue"> = "#0000FF";
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Index Signature Labels

Index Signature Labels allows us to label index signatures using computed property names. It helps in providing more descriptive type information when working with dynamic objects.


type DynamicObject = { [key: string as `dynamic_${string}`]: string };

// Usage:
let obj: DynamicObject = { dynamic_key: "value" };
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5.x also now supports native JavaScript private fields. The TypeScript 'private' still works as discussed in Classes section.