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Mastering TypeScript: A Comprehensive Guide to Writing and Publishing Libraries

Getting Started with TypeScript

To begin, let’s create a new project and install TypeScript using npm:

npm init -y
npm install typescript

Next, we’ll create a tsconfig.json file to configure our TypeScript project. This file will define how our code is compiled and what features are enabled.

Configuring tsconfig.json

The tsconfig.json file is the heart of our TypeScript project. Here, we’ll define the compiler options, module system, and output directory. Let’s take a closer look at some of the key settings:

• target: specifies the level of JavaScript support in the browsers we’re targeting. We’ll set this to ES2015 for modern browsers.
• module: defines the module system we’re using. We’ll set this to ES2020 for modern ES modules.
• outDir: specifies the output directory for our compiled code. We’ll set this to lib for simplicity.

Choosing a Module System

When publishing a library, we need to decide which module system to use. We can choose between ES modules, CommonJS, or even UMD. For this example, we’ll use ES modules, but we’ll also provide a CommonJS version for compatibility.

Exporting Modules

TypeScript provides several ways to export modules. We can use default exports, named exports, or even re-exports. Let’s explore each option:

• Default exports: use the export default syntax to export a single value or function.
• Named exports: use the export syntax to export multiple values or functions.
• Re-exports: use the export syntax to export values or functions from existing modules.

// Default export
export default function add(a: number, b: number) {
  return a + b;
}

// Named export
export function subtract(a: number, b: number) {
  return a - b;
}

// Re-export
export { add as calculate } from './math';

Importing Modules

Now that we’ve exported our modules, let’s see how to import them. We can use the import syntax to import specific exports or entire modules.

import { add } from './math';
import * as math from './math';

Compiling with TypeScript

With our tsconfig.json file configured, we can now compile our code using the tsc command. This will generate JavaScript files in our lib directory.

tsc

Publishing Type Definitions

To provide better type support for our users, we can publish type definitions alongside our code. We’ll add the declaration option to our tsconfig.json file and generate .d.ts files.

Publishing to CommonJS

To provide compatibility with older environments, we’ll also publish a CommonJS version of our library. We’ll create a separate tsconfig-cjs.json file that inherits from our main tsconfig.json file and overrides the module setting.

Preparing to Publish

With our code compiled and type definitions generated, we’re ready to publish our library to npm. We’ll update our package.json file to include the necessary fields, such as main and module, and specify the files to include in our package.

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