# TypeScript development

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 v4.3.0 and above. Existing JavaScript projects can add TypeScript support through a conversion procedure. 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 installation documentation to create a new TypeScript project. For existing projects, TypeScript support can be added with the provided conversion steps. 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:

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

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

// path: ./src/index.ts

import { Strapi } from '@strapi/strapi';

export default {
  register( { strapi }: { strapi: Strapi }) {
    // ...
  },
};

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Within the body of the register method, start typing strapi. and use keyboard arrows to browse the available properties.
Choose runLifecyclesfunction from the list.
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.

# Generate typings for project schemas

To generate typings for your project schemas use the ts:generate-types CLI command. The ts:generate-types command creates the file schemas.d.ts, at the project root, which stores the schema typings. The optional --verbose flag returns a detailed table of the generated schemas.

To use ts:generate-typesrun the following code in a terminal at the project root:

# 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 or npm 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 or npm 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

To start Strapi programmatically in a TypeScript project the Strapi instance requires the compiled code location. This section describes how to set and indicate the compiled code directory.

# Use the `strapi()` factory

Strapi can be run programmatically by using the strapi() factory. Since the code of TypeScript projects is compiled in a specific directory, the parameter distDir should be passed to the factory to indicate where the compiled code should be read:

// path: ./server.js 

const strapi = require('@strapi/strapi');
const app = strapi({ distDir: './dist' });
app.start();

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# Use the `strapi.compile()` function

The strapi.compile() function should be mostly used for developing tools that need to start a Strapi instance and detect whether the project includes TypeScript code. strapi.compile() automatically detects the project language. If the project code contains any TypeScript code, strapi.compile() compiles the code and returns a context with specific values for the directories that Strapi requires:

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

strapi.compile().then(appContext => strapi(appContext).start());

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# Add TypeScript support to an existing Strapi project

Adding TypeScript support to an existing project requires adding 2 tsconfig.json files and rebuilding the admin panel. Additionally, the eslintrc and eslintignore files can be optionally removed. The TypeScript flag allowJs should be set to true in the root tsconfig.json file to incrementally add TypeScript files to existing JavaScript projects. The allowJs flag allows .ts and .tsx files to coexist with JavaScript files.

TypeScript support can be added to an existing Strapi project using the following procedure:

Add a tsconfig.json file at the project root and copy the following code, with the allowJs flag, to the file:

// path: ./tsconfig.json

{
    "extends": "@strapi/typescript-utils/tsconfigs/server",
    "compilerOptions": {
      "outDir": "dist",
      "rootDir": ".",
      "allowJs": true //enables the build without .ts files
    },
    "include": [
      "./",
      "src/**/*.json"
    ],
    "exclude": [
      "node_modules/",
      "build/",
      "dist/",
      ".cache/",
      ".tmp/",
      "src/admin/",
      "**/*.test.ts",
      "src/plugins/**"
    ]
   
  }

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Add a tsconfig.json file in the ./src/admin/ directory and copy the following code to the file:

// path: ./src/admin/tsconfig.json

{
    "extends": "@strapi/typescript-utils/tsconfigs/admin",
    "include": [
      "../plugins/**/admin/src/**/*",
      "./"
    ],
    "exclude": [
      "node_modules/",
      "build/",
      "dist/",
      "**/*.test.ts"
    ]
  }

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(optional) Delete the .eslintrc and .eslintignore files from the project root.
Add an additional '..' to the filename property in the database.ts configuration file (only required for SQLite databases):

//path: ./config/database.ts

const path = require('path');

module.exports = ({ env }) => ({
  connection: {
    client: 'sqlite',
    connection: {
      filename: path.join(__dirname, '..','..', env('DATABASE_FILENAME', '.tmp/data.db')),
    },
    useNullAsDefault: true,
  },
});

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Rebuild the admin panel and start the development server:

After completing the preceding procedure a dist directory will be added at the project root and the project has access to the same TypeScript features as a new TypeScript-supported Strapi project.

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