How to improve performance in mapped types in TypeScript

How to Improve Performance in Mapped Types in TypeScript

When working with TypeScript, you may come across scenarios where you need to transform or manipulate types using mapped types. While mapped types are powerful and flexible, they can sometimes lead to performance issues, especially when dealing with large and complex types. In this article, we will explore some techniques to improve performance when working with mapped types in TypeScript.

1. Use the Readonly modifier

One way to improve performance in mapped types is by using the Readonly modifier. This modifier creates a new type where all properties are marked as read-only, preventing accidental modifications. By using Readonly, TypeScript can optimize the type checking process, resulting in improved performance.

Here’s an example:

type MyType = {
  prop1: string;
  prop2: number;
};

type ReadonlyMyType = Readonly;

const obj: ReadonlyMyType = {
  prop1: "Hello",
  prop2: 42,
};

// obj.prop1 = "World"; // Error: Cannot assign to 'prop1' because it is a read-only property.

2. Use Conditional Types

Another technique to enhance performance in mapped types is by utilizing conditional types. Conditional types allow you to conditionally transform or map types based on certain conditions. By using conditional types, you can avoid unnecessary type transformations, resulting in improved performance.

Here’s an example:

type MyType = {
  prop1: string;
  prop2: number;
  prop3: boolean;
};

type FilteredType = {
  [K in keyof T]: T[K] extends string ? T[K] : never;
};

const obj: FilteredType = {
  prop1: "Hello",
  prop2: 42,
  prop3: true,
};

// obj.prop3 = false; // Error: Type 'false' is not assignable to type 'never'.

3. Use Indexed Access Types

Indexed access types can also contribute to improving performance in mapped types. Indexed access types allow you to access the types of specific properties dynamically. By using indexed access types, TypeScript can optimize the type checking process by directly accessing the required types, resulting in improved performance.

Here’s an example:

type MyType = {
  prop1: string;
  prop2: number;
};

type MyTypeProps = MyType[keyof MyType];

const obj: MyTypeProps = "Hello";

By following these techniques, you can significantly enhance the performance of your mapped types in TypeScript. Remember to analyze your specific use case and choose the most appropriate solution for your scenario.

Happy coding!