If you haven’t already, you should read the TypeScript Handbook to familiarize yourself with basic concepts, especially types and modules.

The most common case for learning how .d.ts files work is that you’re typing an npm package with no types. In that case, you can jump straight to .

We are often faced with writing a declaration file when we only have examples of the underlying library to guide us. The Declaration Reference section shows many common API patterns and how to write declarations for each of them. This guide is aimed at the TypeScript novice who may not yet be familiar with every language construct in TypeScript.

The guide helps you understand common library formats and how to write a proper declaration file for each format. If you’re editing an existing file, you probably don’t need to read this section. Authors of new declaration files are strongly encouraged to read this section to properly understand how the format of the library influences the writing of the declaration file.

Many common mistakes in declaration files can be easily avoided. The Do’s and Don’ts section identifies common errors, describes how to detect them, and how to fix them. Everyone should read this section to help themselves avoid common mistakes.

For seasoned authors interested in the underlying mechanics of how declaration files work, the section explains many advanced concepts in declaration writing, and shows how to leverage these concepts to create cleaner and more intuitive declaration files.

For JavaScript library users, the Consumption section offers a few simple steps to locate and install corresponding declaration files.