TypeScript Node Starter

WebSocket connection

You must connect to the /parties namespace

import client from 'socket.io-client'

const socket = client.connect(`http://localhost:${port}/parties`)

On connection, you will join the party if it exists. Otherwise, it will throw an error. You must create the party before using the REST API endpoint:

POST /parties

Events

• song:submit with a string payload which is the song ID. You will eventually receive a playlist event with the new playlist, to which your song was added. The playlist is a list of strings representing the song IDs.

Intro

The main purpose of this repository is to show a good end-to-end project setup and workflow for writing Node code in TypeScript. We will try to keep this as up-to-date as possible, but community contributions and recommendations for improvements are encouraged and will be most welcome.

Table of contents:

• Pre-reqs
• Getting started
• Deploying the app
  • Pre-reqs
  • Deploying to Azure App Service
• TypeScript + Node
  • Getting TypeScript
  • Project Structure
  • Building the project
  • Type Definition (.d.ts) Files
  • Testing
  • ESLint

Pre-reqs

To build and run this app locally you will need a few things:

• Install Node.js

Getting started

• Install dependencies

cd <project_name>
yarn

• Serve the project

yarn serve

Finally, navigate to http://localhost:3000 and you should see the template being served and rendered locally!

TypeScript + Node

In the next few sections I will call out everything that changes when adding TypeScript to an Express project. Note that all of this has already been setup for this project, but feel free to use this as a reference for converting other Node.js projects to TypeScript.

Getting TypeScript

TypeScript itself is simple to add to any project with npm.

npm install -D typescript

If you're using VS Code then you're good to go! VS Code will detect and use the TypeScript version you have installed in your node_modules folder. For other editors, make sure you have the corresponding TypeScript plugin.

Project Structure

The most obvious difference in a TypeScript + Node project is the folder structure. In a TypeScript project, it's best to have separate source and distributable files. TypeScript (.ts) files live in your src folder and after compilation are output as JavaScript (.js) in the dist folder. The test folder remain top level as expected.

The full folder structure of this app is explained below:

Note! Make sure you have already built the app using npm run build

Name	Description
.vscode	Contains VS Code specific settings
bin	Entry point to the app
dist	Contains the distributable (or output) from your TypeScript build. This is the code you ship
node_modules	Contains all your npm dependencies
src	Contains your source code that will be compiled to the dist dir
src/core	The core components of this API
src/party	All files related to the party resource
src/types	Holds .d.ts files not found on DefinitelyTyped. Covered more in this section
test	Contains your tests. Separate from source because there is a different build process.
.env.example	API keys, tokens, passwords, database URI. Clone this, but don't check it in to public repos.
.travis.yml	Used to configure Travis CI build
jest.config.js	Used to configure Jest running tests written in TypeScript
package.json	File that contains npm dependencies as well as build scripts
tsconfig.json	Config settings for compiling server code written in TypeScript
.eslintrc	Config settings for ESLint code style checking
.eslintignore	Config settings for paths to exclude from linting

Building the project

It is rare for JavaScript projects not to have some kind of build pipeline these days, however Node projects typically have the least amount of build configuration. Because of this I've tried to keep the build as simple as possible. If you're concerned about compile time, the main watch task takes ~2s to refresh.

Configuring TypeScript compilation

TypeScript uses the file tsconfig.json to adjust project compile options. Let's dissect this project's tsconfig.json, starting with the compilerOptions which details how your project is compiled.

{
  "compilerOptions": {
    "module": "commonjs",
    "esModuleInterop": true,
    "allowSyntheticDefaultImports": true,
    "target": "es6",
    "noImplicitAny": true,
    "moduleResolution": "node",
    "sourceMap": true,
    "outDir": "dist",
    "baseUrl": ".",
    "paths": {
      "*": [
        "node_modules/*",
        "src/types/*"
      ]
    }
  },
  "include": [
    "bin/index.ts"
  ],
  "exclude": [
    "node_modules",
    "src/types"
  ]
}

compilerOptions	Description
"module": "commonjs"	The output module type (in your .js files). Node uses commonjs, so that is what we use
"esModuleInterop": true,	Allows usage of an alternate module import syntax: import foo from 'foo';
"target": "es6"	The output language level. Node supports ES6, so we can target that here
"noImplicitAny": true	Enables a stricter setting which throws errors when something has a default any value
"moduleResolution": "node"	TypeScript attempts to mimic Node's module resolution strategy. Read more here
"sourceMap": true	We want source maps to be output along side our JavaScript. See the debugging section
"outDir": "dist"	Location to output .js files after compilation
"baseUrl": "."	Part of configuring module resolution. See path mapping section
paths: {...}	Part of configuring module resolution. See path mapping section

The rest of the file define the TypeScript project context. The project context is basically a set of options that determine which files are compiled when the compiler is invoked with a specific tsconfig.json. In this case, we use the following to define our project context:

"include": [
    "src/**/*"
]

include takes an array of glob patterns of files to include in the compilation. This project is fairly simple and all of our .ts files are under the src folder. For more complex setups, you can include an exclude array of glob patterns that removes specific files from the set defined with include. There is also a files option which takes an array of individual file names which overrides both include and exclude.

Running the build

All the different build steps are orchestrated via npm scripts. Npm scripts basically allow us to call (and chain) terminal commands via npm. This is nice because most JavaScript tools have easy to use command line utilities allowing us to not need grunt or gulp to manage our builds. If you open package.json, you will see a scripts section with all the different scripts you can call. To call a script, simply run npm run <script-name> from the command line. You'll notice that npm scripts can call each other which makes it easy to compose complex builds out of simple individual build scripts. Below is a list of all the scripts this template has available:

Npm Script	Description
start	Does the same as 'npm run serve'. Can be invoked with npm start
prebuild	Removes the dist directory before build.
build	Full build. Runs ALL build tasks (build-ts, lint)
serve	Runs ts-node on bin which is apps entry point
test	Runs tests using Jest test runner
watch-test	Runs tests in watch mode
build-ts	Compiles all source .ts files to .js files in the dist folder
watch-ts	Same as build-ts but continuously watches .ts files and re-compiles when needed
lint	Runs ESLint on project files

Type Definition (.d.ts) Files

TypeScript uses .d.ts files to provide types for JavaScript libraries that were not written in TypeScript. This is great because once you have a .d.ts file, TypeScript can type check that library and provide you better help in your editor. The TypeScript community actively shares all of the most up-to-date .d.ts files for popular libraries on a GitHub repository called DefinitelyTyped. Making sure that your .d.ts files are setup correctly is super important because once they're in place, you get an incredible amount of high quality type checking (and thus bug catching, IntelliSense, and other editor tools) for free.

Note! Because we're using "noImplicitAny": true, we are required to have a .d.ts file for every library we use. While you could set noImplicitAny to false to silence errors about missing .d.ts files, it is a best practice to have a .d.ts file for every library. (Even if the .d.ts file is basically empty!)

Installing .d.ts files from DefinitelyTyped

For the most part, you'll find .d.ts files for the libraries you are using on DefinitelyTyped. These .d.ts files can be easily installed into your project by using the npm scope @types. For example, if we want the .d.ts file for jQuery, we can do so with npm install --save-dev @types/jquery.

Note! Be sure to add --save-dev (or -D) to your npm install. .d.ts files are project dependencies, but only used at compile time and thus should be dev dependencies.

In this template, all the .d.ts files have already been added to devDependencies in package.json, so you will get everything you need after running your first npm install. Once .d.ts files have been installed using npm, you should see them in your node_modules/@types folder. The compiler will always look in this folder for .d.ts files when resolving JavaScript libraries.

What if a library isn't on DefinitelyTyped?

If you try to install a .d.ts file from @types and it isn't found, or you check DefinitelyTyped and cannot find a specific library, you will want to create your own .d.ts file. In the src folder of this project, you'll find the types folder which holds the .d.ts files that aren't on DefinitelyTyped (or weren't as of the time of this writing).

Setting up TypeScript to look for .d.ts files in another folder

The compiler knows to look in node_modules/@types by default, but to help the compiler find our own .d.ts files we have to configure path mapping in our tsconfig.json. Path mapping can get pretty confusing, but the basic idea is that the TypeScript compiler will look in specific places, in a specific order when resolving modules, and we have the ability to tell the compiler exactly how to do it. In the tsconfig.json for this project you'll see the following:

"baseUrl": ".",
"paths": {
    "*": [
        "node_modules/*",
        "src/types/*"
    ]
}

This tells the TypeScript compiler that in addition to looking in node_modules/@types for every import (*) also look in our own .d.ts file location <baseUrl> + src/types/*. So when we write something like:

import * as flash from "express-flash";

First the compiler will look for a d.ts file in node_modules/@types and then when it doesn't find one look in src/types and find our file express-flash.d.ts.

Using dts-gen

Unless you are familiar with .d.ts files, I strongly recommend trying to use the tool dts-gen first. The README does a great job explaining how to use the tool, and for most cases, you'll get an excellent scaffold of a .d.ts file to start with. In this project, bcrypt-nodejs.d.ts, fbgraph.d.ts, and lusca.d.ts were all generated using dts-gen.

Writing a .d.ts file

If generating a .d.ts using dts-gen isn't working, you should tell me about it first, but then you can create your own .d.ts file.

If you just want to silence the compiler for the time being, create a file called <some-library>.d.ts in your types folder and then add this line of code:

declare module "<some-library>";

If you want to invest some time into making a great .d.ts file that will give you great type checking and IntelliSense, the TypeScript website has great docs on authoring .d.ts files.

Contributing to DefinitelyTyped

The reason it's so easy to get great .d.ts files for most libraries is that developers like you contribute their work back to DefinitelyTyped. Contributing .d.ts files is a great way to get into the open source community if it's something you've never tried before, and as soon as your changes are accepted, every other developer in the world has access to your work.

If you're interested in giving it a shot, check out the guidance on DefinitelyTyped. If you're not interested, you should tell me why so we can help make it easier in the future!

Summary of .d.ts management

In general if you stick to the following steps you should have minimal .d.ts issues;

1. After installing any npm package as a dependency or dev dependency, immediately try to install the .d.ts file via @types.
2. If the library has a .d.ts file on DefinitelyTyped, the install will succeed and you are done. If the install fails because the package doesn't exist, continue to step 3.
3. Make sure you project is configured for supplying your own d.ts files
4. Try to generate a .d.ts file with dts-gen. If it succeeds, you are done. If not, continue to step 5.
5. Create a file called <some-library>.d.ts in your types folder.
6. Add the following code:

declare module "<some-library>";

7. At this point everything should compile with no errors and you can either improve the types in the .d.ts file by following this guide on authoring .d.ts files or continue with no types.
8. If you are still having issues, let me know by sending me an email or pinging me on twitter, I will help you.

Debugging

Debugging TypeScript is exactly like debugging JavaScript with one caveat, you need source maps.

Source maps

Source maps allow you to drop break points in your TypeScript source code and have that break point be hit by the JavaScript that is being executed at runtime.

Note! - Source maps aren't specific to TypeScript. Anytime JavaScript is transformed (transpiled, compiled, optimized, minified, etc) you need source maps so that the code that is executed at runtime can be mapped back to the source that generated it.

The best part of source maps is when configured correctly, you don't even know they exist! So let's take a look at how we do that in this project.

Configuring source maps

First you need to make sure your tsconfig.json has source map generation enabled:

"compilerOptions" {
    "sourceMap": true
}

With this option enabled, next to every .js file that the TypeScript compiler outputs there will be a .map.js file as well. This .map.js file provides the information necessary to map back to the source .ts file while debugging.

Note! - It is also possible to generate "inline" source maps using "inlineSourceMap": true. This is more common when writing client side code because some bundlers need inline source maps to preserve the mapping through the bundle. Because we are writing Node.js code, we don't have to worry about this.

Testing

For this project, We chose Jest as our test framework.

Install the components

To add TypeScript + Jest support, first install a few npm packages:

npm install -D jest ts-jest

jest is the testing framework itself, and ts-jest is just a simple function to make running TypeScript tests a little easier.

Configure Jest

Jest's configuration lives in jest.config.js, so let's open it up and add the following code:

module.exports = {
  globals: {
    'ts-jest': {
      tsConfig: 'tsconfig.json'
    }
  },
  moduleFileExtensions: ['ts', 'js'],
  transform: {
    '^.+\\.(ts|tsx)$': 'ts-jest'
  },
  testMatch: ['<rootDir>/src/**/*.test.(ts|js)'],
  testEnvironment: 'node'
}

Basically we are telling Jest that we want it to consume all files that match the pattern "**/test/**/*.test.(ts|js)" (all .test.ts/.test.js files in the test folder), but we want to preprocess the .ts files first. This preprocess step is very flexible, but in our case, we just want to compile our TypeScript to JavaScript using our tsconfig.json. This all happens in memory when you run the tests, so there are no output .js test files for you to manage.

Running tests

Simply run npm run test. Note this will also generate a coverage report.

ESLint

ESLint is a code linter which mainly helps catch quickly minor code quality and style issues.

ESLint rules

Like most linters, ESLint has a wide set of configurable rules as well as support for custom rule sets. All rules are configured through .eslintrc configuration file.

Running ESLint

Like the rest of our build steps, we use npm scripts to invoke ESLint. To run ESLint you can call the main build script or just the ESLint task.

npm run build   // runs full build including ESLint
npm run lint    // runs only ESLint

Notice that ESLint is not a part of the main watch task.