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Mastering TypeScript
Advanced TypeScript patterns and best practices
John Smith
Mastering TypeScript
TypeScript has become the de facto standard for large-scale JavaScript applications. In this guide, we'll explore advanced patterns and best practices that will take your TypeScript skills to the next level.
Advanced Type System Features
Conditional Types
Conditional types allow you to create types that depend on other types:
type IsString<T> = T extends string ? true : false;
type A = IsString<string>; // true
type B = IsString<number>; // falseTemplate Literal Types
Template literal types provide a way to manipulate string types:
type Greeting<T extends string> = `Hello, ${T}!`;
type WelcomeMessage = Greeting<"World">; // "Hello, World!"Utility Types Deep Dive
Creating Custom Utility Types
type DeepReadonly<T> = {
readonly [P in keyof T]: T[P] extends object
? DeepReadonly<T[P]>
: T[P];
};Advanced Mapped Types
type Getters<T> = {
[K in keyof T as `get${Capitalize<string & K>}`]: () => T[K]
};
interface Person {
name: string;
age: number;
}
type PersonGetters = Getters<Person>;
// { getName: () => string; getAge: () => number; }Type Guards and Narrowing
User-Defined Type Guards
interface Bird {
fly(): void;
layEggs(): void;
}
interface Fish {
swim(): void;
layEggs(): void;
}
function isFish(pet: Fish | Bird): pet is Fish {
return (pet as Fish).swim !== undefined;
}Using the satisfies Operator
type Colors = "red" | "green" | "blue";
type RGB = [red: number, green: number, blue: number];
const palette = {
red: [255, 0, 0],
green: "#00ff00",
blue: [0, 0, 255]
} satisfies Record<Colors, string | RGB>;Generics Best Practices
Constraining Generics
function getProperty<T, K extends keyof T>(obj: T, key: K): T[K] {
return obj[key];
}Generic Inference
function map<T, U>(array: T[], fn: (item: T) => U): U[] {
return array.map(fn);
}
// TypeScript infers the types
const numbers = [1, 2, 3];
const strings = map(numbers, n => n.toString());Module Patterns
Namespace Augmentation
declare module "express" {
interface Request {
user?: {
id: string;
email: string;
};
}
}Error Handling Patterns
Result Type Pattern
type Result<T, E = Error> =
| { success: true; value: T }
| { success: false; error: E };
function divide(a: number, b: number): Result<number, string> {
if (b === 0) {
return { success: false, error: "Division by zero" };
}
return { success: true, value: a / b };
}Performance Considerations
Type-Level Optimization
- Use
interfaceovertypewhen possible for better performance - Avoid deeply nested conditional types
- Be mindful of type instantiation depth
Conclusion
TypeScript's type system is incredibly powerful and expressive. By mastering these advanced patterns, you'll be able to write more robust, maintainable, and self-documenting code. Remember, the goal is not to use every feature, but to choose the right tool for the job.
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