# TypeScript development

🚧 TypeScript documentation

This section is still a work in progress and will continue to be updated and improved. Migrating existing Strapi applications written in JavaScript is not currently recommended. In the meantime, feel free to ask for help on the forum (opens new window) or on the community Discord (opens new window).

TypeScript adds an additional type system layer above JavaScript, which means that existing JavaScript code is also TypeScript code. Strapi supports TypeScript in new projects on v4.2.0 and above. TypeScript-enabled projects allow developing plugins with TypeScript as well as using TypeScript typings.

🤓 Getting started with TypeScript

To start developing in TypeScript, use the CLI documentation to create a new TypeScript project. Additionally, the project structure and TypeScript configuration sections have TypeScript-specific resources for understanding and configuring an application.

# Start developing in TypeScript

Starting the development environment for a TypeScript-enabled project requires building the admin panel prior to starting the server. In development mode, the application source code is compiled to the ./dist/build directory and recompiled with each change in the Content-type Builder. To start the application, run the following commands in the root directory:

# Use TypeScript typings

Strapi provides typings on the Strapi class to improve the TypeScript developing experience. These typings come with an autocomplete feature that automatically offers suggestions while developing.

To experience TypeScript-based autocomplete while developing Strapi applications, you could try the following:

  1. From your code editor, open the ./src/index.ts file.

  2. In the register method, declare the strapi argument as of type Strapi:

    // path: ./src/index.ts
    
    import '@strapi/strapi';
    
    export default {
      register( { strapi }: { strapi: Strapi }) {
        // ...
      },
    };
    
  3. Within the body of the register method, start typing strapi. and use keyboard arrows to browse the available properties.

  4. Choose runLifecyclesfunction from the list.

  5. When the strapi.runLifecyclesFunctions method is added, a list of available lifecycle types (i.e. register, bootstrap and destroy) are returned by the code editor. Use keyboard arrows to choose one of the lifecycles and the code will autocomplete.

# Develop a plugin using TypeScript

New plugins can be generated following the plugins development documentation. There are 2 important distinctions for TypeScript applications:

  • After creating the plugin, run yarn install or npm run install in the plugin directory src/admin/plugins/[my-plugin-name] to install the dependencies for the plugin.
  • Run yarn build or npm run build in the plugin directory src/admin/plugins/[my-plugin-name] to build the admin panel including the plugin.

✏️ NOTE

It is not necessary to repeat the yarn install or npm run install command after the initial installation. The yarn build or npm run build command is necessary to implement any plugin development that affects the admin panel.

# Start Strapi programmatically

Instantiating Strapi programmatically in a TypeScript project requires additional configurations to load everything correctly. The primary difference for TypeScript programmatic use is that the codebase and compiled code are stored in separate directories, whereas the same directory is used to read and write in native JavaScript.

# Understand programatic use

When instantiating Strapi programmatically using the default export of @strapi/strapi, different parameters such as the app directory and the dist directory can be passed. The app directory is the project root directory and dist is a subdirectory of app. The dist directory represents the compiled project, with the same directory structure as the app directory, and the app directory represents the codebase (TypeScript or JavaScript). The main differences are:

  • When using the Content-type Builder to create, update, delete content types (or any other service that creates files), Strapi uses the app folder to write the files.
  • When reading what content types exist on the system Strapi reads the dist folder.
  • When the develop command is used only the app directory is watched. In TypeScript, a compilation will be triggered when a change is detected in the app directory and the output will be written to the dist directory.

✏️ NOTE

The public folder is considered static and thus ignores the app and dist directories.

The default values for the app and dist directories are transformed and assigned using one of the following options:


const resolveWorkingDirectories = opts => {
  const cwd = process.cwd(); // Neither the appDir or distDir are passed. Both the appDir and distDir are set to process.cwd().

  const appDir = opts.appDir ? path.resolve(cwd, opts.appDir) : cwd; // Only appDir is defined distDir matches appDir.
  
  const distDir = opts.distDir ? path.resolve(cwd, opts.distDir) : appDir; // Only distDir is defined, appDir is set to process.cwd().

  return { appDir, distDir };
}

For example, if the compiled code is stored in a separate directory (eg: when using TypeScript) Strapi should be instantiated with a specific distDir value which matches the path of your build directory.

✋ CAUTION

Do not set the appDir to the build or dist directory as it could cause issues when the app tries to write some files.

# Start Strapi programmatically examples

Start Strapi for JavaScript applications:

const strapi = require('@strapi/strapi');

strapi();
// appDir => process.cwd() | distDir => process.cwd()

Start Strapi using a custom dist directory:

const strapi = require('@strapi/strapi');

strapi({ distDir: './dist' });
// appDir => process.cwd() | distDir => './dist'

Start Strapi using custom app and dist directories:


const strapi = require('@strapi/strapi');

strapi({ distDir: './dist' });
// appDir => process.cwd() | distDir => './dist'

Start Strapi using a custom app directory:


const strapi = require('@strapi/strapi');

strapi({ appDir: './app' });
// appDir => './app' | distDir => './app'

# Use both JavaScript and TypeScript codebases when starting Strapi programmatically

Adding the package @strapi/typescript-utils allows for both JavaScript and TypeScript codebases to be used programatically. A common use is for creating command line interface tools or developing a plugin. Examples of how to incorporate both code bases:

const tsUtils = require('@strapi/typescript-utils');
const strapi = require('@strapi/strapi');

const appDir = process.cwd();

// Automatically detect if this is a Typescript project:
const isTSProject = await tsUtils.isUsingTypeScript(appDir);

// Resolve the directory containing the compilation output:
const outDir = await tsUtils.resolveOutDir(appDir);

if (isTSProject) {
// If inside a Typescript project, compile the TypeScript code in the appDir:
  await tsUtils.compile(appDir, {
    watch: false,
    configOptions: { options: { incremental: true } },
  });
}

// If inside a Typescript project, use a custom dist directory, otherwise set it to appDir value: 
const distDir = isTSProject ? outDir : appDir;

// Start the app by providing the app and dist directories:
const app = await strapi({ appDir, distDir }).load();