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Using TypeScript ​

While CAP itself is written in JavaScript, it's possible to use TypeScript within your project as outlined here.

Enable TypeScript Support ​

Follow these steps to add TypeScript support:

  1. Install typescript packages globally:

    sh
    npm i -g typescript ts-node

  2. Add a basic tsconfig.json file to your project:

    sh
    cds add typescript

    You can modify this configuration file to match your project setup. See the official TypeScript documentation for more details. Note that adding the typescript facet, cds-typer is also automatically added to your project.

Writing TypeScript Files ​

Once you have setup everything correctly, you can start using TypeScript files instead of JavaScript files. This setup applies for service handlers, and to a custom server.ts file, or database init.ts seeding files as well.

Samples ​

For a full TypeScript application, check out the SFlight application. It features both CAP service handlers and client-side code for SAP Fiori Elements written in TypeScript.

Developing TypeScript Projects ​

Using cds watch since @sap/cds-dk 8.6.0 ​

Preferably use cds watch in a TypeScript project as if it was a JavaScript project. It detects TypeScript mode based on a tsconfig.json and run cds-tsx under the hood.

sh
cap/sflight $ cds watch

Detected tsconfig.json. Running with tsx.
...
[cds] serving TravelService { impl: 'srv/travel-service.ts', path: '/processor' }
...

The same applies to cds serve.

Using cds-tsx since @sap/cds-dk 8.2.0 ​

Alternatively, you can use the cds-tsx CLI command instead of cds for automatic TypeScript transpilation:

sh
cds-tsx watch
sh
cds-tsx serve

Under the hood, the tsx engine is used to run the files instead of the default node engine. Install it globally with:

sh
npm i -g tsx

Not for production

Use cds-watch and cds-tsx / tsx during development only. For productive usage, always precompile TypeScript code to JavaScript for best performance and use cds-serve as usual.

Using cds-ts ​

Much like cds-tsx, you can also use the cds-ts CLI command:

sh
cds-ts watch
sh
cds-ts serve

It uses the ts-node engine under the hood.

tsx or ts-node?

In general, tsx is the better choice, as tsx is considerably faster than ts-node because it doesn't perform type checks. See a closer comparison between the two of them.

Testing with ts-jest ​

Run your Jest tests with preset ts-jest without precompiling TypeScript files.

  1. Install ts-jest locally:

    sh
    npm install -D ts-jest

  2. Tell Jest to use the preset ts-jest, for example, in your jest.config.js:

    js
    module.exports = {
  preset: "ts-jest",
  globalSetup: "./test/setup.ts"
};

  3. Set CDS_TYPESCRIPT environment variable:

    This is necessary, because it isn't possible to programmatically detect that the preset ts-jest is used and we've to know whether we need to look for .ts or .js files.

    File ./test/setup.ts, content:

    js
    module.exports = async () => {
  process.env.CDS_TYPESCRIPT = "true";
};

  4. Run your tests as usual:

    sh
    jest

Building TypeScript Projects ​

A dedicated build task for cds build is provided as part of the cds-typer package.

Learn more about integrating it into your build process.

TypeScript APIs in @sap/cds since @sap/cds 8.0.0 ​

The package @cap-js/cds-types contains all TypeScript declarations for @sap/cds APIs. These declarations are used automatically when you write TypeScript files, but also enable IntelliSense and type checking for standard JavaScript development in Visual Studio Code. Just add the @cap-js/cds-types package to your project as follows:

sh
npm add @cap-js/cds-types

Use the Typescript declarations like this:

ts
import { Request } from '@sap/cds'

function myHandler(req: Request) { }

Types are available even in JavaScript through JSDoc comments:

js
/**
 * @param { import('@sap/cds').Request } req
 */
function myHandler(req) { }

Type Imports ​

Import types through the cds facade class only:

Good: ​
ts
import { ... } from '@sap/cds'
Bad: ​

Never code against paths inside @sap/cds/apis/:

ts
import { ... } from '@sap/cds/apis/events'

Community ​

Help us improve the types ​

We invite you to contribute and help us complete the typings as appropriate. Find the sources on GitHub and open a pull request or an issue.

Still, as @sap/cds is a JavaScript library, typings aren't always up to date. You should expect a delay for typings related to the latest release, even gaps, and errors.

Generating Model Types Automatically ​

The cds-typer package offers a way to derive TypeScript definitions from a CDS model to give you enhanced code completion and a certain degree of type safety when implementing services.

js
class CatalogService extends cds.ApplicationService { init() {
    const { Book } = require('#cds-models/sap/capire/bookshop')

    this.before('CREATE', Book, req => {
        req.data.…  // known to be a Book. Code completion suggests:
              // ID (number)
              // title (string)
              // author (Author)
              // createdAt (Date)
              // …
    })
}}

You can find extensive documentation in a dedicated chapter, together with a quickstart guide to get everything up and running.

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