In this article we will set up an Express application using Typescript.

Requirements

In order to follow this tutorial you will need the latest version of Node js installed. I recommend installing node js via Homebrew if you are on OSX. Once node is installed, we can initialise our project using NPM.

Optionally you should install Visual Studio Code. This is a code editor from Microsoft that is built using Typescript. It provides an excellent environment for working with Typescript and many other programming languages.

Setting Up a Typescript Project

Now that the prerequisites are installed we can begin setting up the Typescript project. Open up a terminal, create, and cd into a directory called express-ts. In this directory we will initialize our npm project.

Use the following commands to do so:

mkdir express-ts
cd express-ts
npm --init -y

Now that we are in the created directory and we have initialised our npm project we will install Typescript and generate a tsconfig.json. To do this we must install Typescript as a project dependency.

Run the following command to do so:

npm install --save typescript

Now that Typescript is installed as a dependency we can initialise our Typescript project via npm.

Firstly we must tell npm to use the project’s version of tsc, the Typescript compiler. To do this update the generated package.json file to the following, which aliases tsc to the project’s version of tsc.

{  
  "dependencies": {
    "typescript": "^2.7.1"
  },
  "scripts": {
    "tsc": "tsc"
  }
}

By adding "tsc": "tsc" inside scripts we can run the following command, which will generate a default tsconfig.json file.

npm run tsc -- --init

Running the above command creates the tsconfig.json in the current directory. It also adds some useful boilerplate code to the file. Looking inside the newly generated tsconfig.json you should see the following.

{
  "compilerOptions": {
    /* Basic Options */
    "target": "es5",                          /* Specify ECMAScript target version: 'ES3' (default), 'ES5', 'ES2015', 'ES2016', 'ES2017','ES2018' or 'ESNEXT'. */
    "module": "commonjs",                     /* Specify module code generation: 'none', 'commonjs', 'amd', 'system', 'umd', 'es2015', or 'ESNext'. */
    // "lib": [],                             /* Specify library files to be included in the compilation. */
    // "allowJs": true,                       /* Allow javascript files to be compiled. */
    // "checkJs": true,                       /* Report errors in .js files. */
    // "jsx": "preserve",                     /* Specify JSX code generation: 'preserve', 'react-native', or 'react'. */
    // "declaration": true,                   /* Generates corresponding '.d.ts' file. */
    // "sourceMap": true,                     /* Generates corresponding '.map' file. */
    // "outFile": "./",                       /* Concatenate and emit output to single file. */
    // "outDir": "./",                        /* Redirect output structure to the directory. */
    // "rootDir": "./",                       /* Specify the root directory of input files. Use to control the output directory structure with --outDir. */
    // "removeComments": true,                /* Do not emit comments to output. */
    // "noEmit": true,                        /* Do not emit outputs. */
    // "importHelpers": true,                 /* Import emit helpers from 'tslib'. */
    // "downlevelIteration": true,            /* Provide full support for iterables in 'for-of', spread, and destructuring when targeting 'ES5' or 'ES3'. */
    // "isolatedModules": true,               /* Transpile each file as a separate module (similar to 'ts.transpileModule'). */

    /* Strict Type-Checking Options */
    "strict": true,                           /* Enable all strict type-checking options. */
    // "noImplicitAny": true,                 /* Raise error on expressions and declarations with an implied 'any' type. */
    // "strictNullChecks": true,              /* Enable strict null checks. */
    // "strictFunctionTypes": true,           /* Enable strict checking of function types. */
    // "strictPropertyInitialization": true,  /* Enable strict checking of property initialization in classes. */
    // "noImplicitThis": true,                /* Raise error on 'this' expressions with an implied 'any' type. */
    // "alwaysStrict": true,                  /* Parse in strict mode and emit "use strict" for each source file. */

    /* Additional Checks */
    // "noUnusedLocals": true,                /* Report errors on unused locals. */
    // "noUnusedParameters": true,            /* Report errors on unused parameters. */
    // "noImplicitReturns": true,             /* Report error when not all code paths in function return a value. */
    // "noFallthroughCasesInSwitch": true,    /* Report errors for fallthrough cases in switch statement. */

    /* Module Resolution Options */
    // "moduleResolution": "node",            /* Specify module resolution strategy: 'node' (Node.js) or 'classic' (TypeScript pre-1.6). */
    // "baseUrl": "./",                       /* Base directory to resolve non-absolute module names. */
    // "paths": {},                           /* A series of entries which re-map imports to lookup locations relative to the 'baseUrl'. */
    // "rootDirs": [],                        /* List of root folders whose combined content represents the structure of the project at runtime. */
    // "typeRoots": [],                       /* List of folders to include type definitions from. */
    // "types": [],                           /* Type declaration files to be included in compilation. */
    // "allowSyntheticDefaultImports": true,  /* Allow default imports from modules with no default export. This does not affect code emit, just typechecking. */
    "esModuleInterop": true                   /* Enables emit interoperability between CommonJS and ES Modules via creation of namespace objects for all imports. Implies 'allowSyntheticDefaultImports'. */
    // "preserveSymlinks": true,              /* Do not resolve the real path of symlinks. */

    /* Source Map Options */
    // "sourceRoot": "./",                    /* Specify the location where debugger should locate TypeScript files instead of source locations. */
    // "mapRoot": "./",                       /* Specify the location where debugger should locate map files instead of generated locations. */
    // "inlineSourceMap": true,               /* Emit a single file with source maps instead of having a separate file. */
    // "inlineSources": true,                 /* Emit the source alongside the sourcemaps within a single file; requires '--inlineSourceMap' or '--sourceMap' to be set. */

    /* Experimental Options */
    // "experimentalDecorators": true,        /* Enables experimental support for ES7 decorators. */
    // "emitDecoratorMetadata": true,         /* Enables experimental support for emitting type metadata for decorators. */
  }
}

For the purposes of this demo we are going to put the compiled .js files into a build directory. In order to tell the Typescript compiler that this is where the compiled files should go we must use the outDir parameter. Uncomment the outDir parameter and give it the value "./build", it should look like the following.

"outDir": "./build",

Now that the tsconfig is correctly set up we will add some Typescript Definition files or .d.ts files via the @types module. These files are used to give the compiler knowledge of the application.

As we will be using Express and ES2015 syntax. We need to install the es6-shim, and express typings. Run the following command to do so.

npm install --save @types/express @types/es6-shim

Now we can install express via NPM. In the application root folder run the following.

npm install --save express

This installs Express as a dependency.

Finally lets create the application files. Make a folder called app and add a server.ts file. The application will be a greeter. So lets also add a WelcomeController. Inside the app folder create another folder called controllers and a welcome.controller.ts and index.ts file.

mkdir app && cd app
touch server.ts
mkdir controllers && cd controllers
touch index.ts welcome.controller.ts

The application should now have the following structure.

.
├── app
│   ├── controllers
│   │   ├── index.ts
│   │   └── welcome.controller.ts
│   └── server.ts
├── node_modules
├── package.json
└── tsconfig.json

Creating An Express App

As mentioned above we will be creating a greeting app. This app will have one route that takes a name parameter and then greets that name.

Open a text editor inside the application folder. If you are using Visual Studio Code you can open it inside the folder by running the code command with a folder argument.

code .

Firstly lets take a look at the welcome.controller.ts file. This file will handle the welcome routes. To do this we need it to export an Express router object. I have added code comments to the snippet below which explains how this file should work.

/* app/controllers/welcome.controller.ts */

// Import only what we need from express
import { Router, Request, Response } from 'express';

// Assign router to the express.Router() instance
const router: Router = Router();

// The / here corresponds to the route that the WelcomeController
// is mounted on in the server.ts file.
// In this case it's /welcome
router.get('/', (req: Request, res: Response) => {
    // Reply with a hello world when no name param is provided
    res.send('Hello, World!');
});

router.get('/:name', (req: Request, res: Response) => {
    // Extract the name from the request parameters
    let { name } = req.params;

    // Greet the given name
    res.send(`Hello, ${name}`);
});

// Export the express.Router() instance to be used by server.ts
export const WelcomeController: Router = router;

Now that the WelcomeController is ready to be used lets export it from the controllers folder. As you may know index files act as folder entry points. Thanks to this we can access exports from the index.ts file we created in the controllers folder. Add the following to that file.

/* app/controllers/index.ts */
export * from './welcome.controller';

Note: as good practice you should never add application logic inside an index file.

Now that the WelcomeController is being correctly exported lets make use of it inside the server.ts file.

/* app/server.ts */

// Import everything from express and assign it to the express variable
import * as express from 'express';

// Import WelcomeController from controllers entry point
import {WelcomeController} from './controllers';

// Create a new express application instance
const app: express.Application = express();
// The port the express app will listen on
const port: number = process.env.PORT || 3000;

// Mount the WelcomeController at the /welcome route
app.use('/welcome', WelcomeController);

// Serve the application at the given port
app.listen(port, () => {
    // Success callback
    console.log(`Listening at http://localhost:${port}/`);
});

Now that we have finished writing the application lets transpile it to javascript. In the root of the application run the following.

npm run tsc

Alternatively you may run the following to tell the Typescript compiler to run everytime it detects a filesystem change.

npm run tsc -- --watch

These commands will tell the Typescript compiler to build the application based on the tsconfig.json. If everything has been successfull you will see a newly created build directory. This is where the Typescript compiler has placed the generated .js files based of the optional outDir parameter in the tsconfig.

We can now run the app with the following command.

node build/server.js

Open a browser at the following url http://localhost:3000/welcome. You should be greeted with a Hello, World!. Try visiting http://localhost:3000/welcome/Borris to confirm the WelcomeController is functioning correctly. You should see a Hello, Borris!.

Summary

This application, though simple, gives a good basis for creating future Express applications with Typescript.

You have learned how to intialise a Typescript application from the command line. You have also seen how to make use of Typings within a Typescript application. Learning how to use typings is very important when working with Typescript as they give the compiler a better knowledge of the application. The more the compiler knows, the better it can help you out.

You have also learned a bit about structuring an Express application. Many Express tutorials bundle code into one big server.js file. This leads to an application that is very difficult to maintain and is not representative of real world applications. However we have seen here that it is possible to mount Express Router instances so that applications can be broken down into modular parts. This leads to more maintainable and scalable applications.

Next Steps?

Working with data is an important skill to learn when using Node. So, with the knowledge gained here I would recommend investigating using Express and Typescript with the Sequelize ORM. It is an awesome NPM package which lets a Node app easily communicate with an SQL database. This will allow you to create dynamic and data driven Node apps.


Finished application files can be found on github at the below link.

https://github.com/BrianDGLS/express-ts