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TypeScript is an extension of the JavaScript language that uses JavaScript’s runtime with a compile-time type checker. This combination allows developers to use the full JavaScript ecosystem and language features, while also adding optional static type-checking, enums, classes, and interfaces on top of it.
Though the pre-made, basic types in TypeScript will cover many use cases, creating your own custom types based on these basic types will allow you to ensure the type checker validates the data structures specific to your project. This will reduce the chance of bugs in your project, while also allowing for better documentation of the data structures used throughout the code.
This tutorial will show you how to use custom types with TypeScript, how to compose those types together with unions and intersections, and how to use utility types to add flexibility to your custom types. It will lead you through different code samples, which you can follow in your own TypeScript environment or the TypeScript Playground, an online environment that allows you to write TypeScript directly in the browser.
Beyond core TypeScript, modern AI coding assistants like GitHub Copilot and Codeium can accelerate type definition and enforcement at scale. In this tutorial, you’ll pair AI-assisted completions and refactors with strict compiler options, runtime validation, code generation from API schemas, governance controls, and CI automation to reliably maintain type safety across large projects and monorepos.
Key Takeaways:
type, add optional properties (?), and use index signatures or Record for flexible key/value maps.|) and intersections (&), and enforce exhaustiveness with discriminated unions and never checks in switch statements.[string, string, ...string[]]).value is T), in/instanceof, and control-flow analysis over as assertions.Record, Pick, Omit, and Partial to transform shapes without rewriting types.zod) to enforce data shape at the boundaries.openapi-typescript, @graphql-codegen/cli), and block merges when generated files drift.strict, noImplicitAny, strictNullChecks, exactOptionalPropertyTypes, noUncheckedIndexedAccess), and enforce hygiene with typescript-eslint rules.tsc --noEmit and ESLint to CI, and pre-commit hooks to run codegen and validate to keep types in sync.Thanks for learning with the DigitalOcean Community. Check out our offerings for compute, storage, networking, and managed databases.
TypeScript is an extension of the JavaScript language that uses JavaScript’s runtime with a compile-time type checker. This combination allows developers to use the full JavaScript ecosystem and language features, while also adding optional static type-checking, enum data types, classes, and interfaces.
This series will show you the syntax you need to get started with TypeScript, allowing you to leverage its typing system to make scalable, enterprise-grade code.
Browse Series: 9 tutorials
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With over 6 years of experience in tech publishing, Mani has edited and published more than 75 books covering a wide range of data science topics. Known for his strong attention to detail and technical knowledge, Mani specializes in creating clear, concise, and easy-to-understand content tailored for developers.
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Custom types in TypeScript help developers define clear and reusable data structures, making code easier to understand and maintain. Instead of repeatedly specifying the shape of an object, you can create a custom type and use it throughout your application.
One common way to create a custom type is with the type keyword:
type User = {
id: number;
name: string;
email: string;
};
Custom types provide several benefits:
type Status = "active" | "inactive";
This restricts values to specific options, improving reliability. For larger projects, custom types help organize complex data models and ensure that developers follow the same structure throughout the codebase. Whether you’re building APIs, web applications, or reusable libraries, custom types are an important feature that improves maintainability and makes TypeScript code more predictable and easier to work with.
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