Express with Typescript

Updated: 03 September 2023

Based on this Medium Article

Introduction

Typescript is basically statically typed ES6 with the ability to compile to javascript, this allows us to code in a manner that better equips us to catch type errors before runtime

Setting Up a Typescript Application

A New Application

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npm init
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npm install typescript -a

Initialising a Typescript Project

In the package.json add a script to run typescript

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"scripts": {
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    "tsc": "tsc"
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},

We can then generate the tsconfig.json file with

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npm run tsc -- --init

After which we can uncomment the outDir property in the tsconfig.json file to specify where to put the Javascript output

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{
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  "compilerOptions": {
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    /* Basic Options */
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    "target": "es5",                          /* Specify ECMAScript target version: 'ES3' (default), 'ES5', 'ES2015', 'ES2016', 'ES2017','ES2018' or 'ESNEXT'. */
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    "module": "commonjs",                     /* Specify module code generation: 'none', 'commonjs', 'amd', 'system', 'umd', 'es2015', or 'ESNext'. */
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    // "lib": [],                             /* Specify library files to be included in the compilation. */
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    // "allowJs": true,                       /* Allow javascript files to be compiled. */
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    // "checkJs": true,                       /* Report errors in .js files. */
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    // "jsx": "preserve",                     /* Specify JSX code generation: 'preserve', 'react-native', or 'react'. */
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    // "declaration": true,                   /* Generates corresponding '.d.ts' file. */
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    // "declarationMap": true,                /* Generates a sourcemap for each corresponding '.d.ts' file. */
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    // "sourceMap": true,                     /* Generates corresponding '.map' file. */
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    // "outFile": "./",                       /* Concatenate and emit output to single file. */
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    "outDir": "./build",                        /* Redirect output structure to the directory. */
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    // "rootDir": "./",                       /* Specify the root directory of input files. Use to control the output directory structure with --outDir. */
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    // "composite": true,                     /* Enable project compilation */
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    // "removeComments": true,                /* Do not emit comments to output. */
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    // "noEmit": true,                        /* Do not emit outputs. */
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    // "importHelpers": true,                 /* Import emit helpers from 'tslib'. */
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    // "downlevelIteration": true,            /* Provide full support for iterables in 'for-of', spread, and destructuring when targeting 'ES5' or 'ES3'. */
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    // "isolatedModules": true,               /* Transpile each file as a separate module (similar to 'ts.transpileModule'). */
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    /* Strict Type-Checking Options */
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    "strict": true,                           /* Enable all strict type-checking options. */
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    // "noImplicitAny": true,                 /* Raise error on expressions and declarations with an implied 'any' type. */
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    // "strictNullChecks": true,              /* Enable strict null checks. */
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    // "strictFunctionTypes": true,           /* Enable strict checking of function types. */
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    // "strictPropertyInitialization": true,  /* Enable strict checking of property initialization in classes. */
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    // "noImplicitThis": true,                /* Raise error on 'this' expressions with an implied 'any' type. */
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    // "alwaysStrict": true,                  /* Parse in strict mode and emit "use strict" for each source file. */
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    /* Additional Checks */
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    // "noUnusedLocals": true,                /* Report errors on unused locals. */
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    // "noUnusedParameters": true,            /* Report errors on unused parameters. */
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    // "noImplicitReturns": true,             /* Report error when not all code paths in function return a value. */
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    // "noFallthroughCasesInSwitch": true,    /* Report errors for fallthrough cases in switch statement. */
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    /* Module Resolution Options */
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    // "moduleResolution": "node",            /* Specify module resolution strategy: 'node' (Node.js) or 'classic' (TypeScript pre-1.6). */
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    // "baseUrl": "./",                       /* Base directory to resolve non-absolute module names. */
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    // "paths": {},                           /* A series of entries which re-map imports to lookup locations relative to the 'baseUrl'. */
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    // "rootDirs": [],                        /* List of root folders whose combined content represents the structure of the project at runtime. */
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    // "typeRoots": [],                       /* List of folders to include type definitions from. */
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    // "types": [],                           /* Type declaration files to be included in compilation. */
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    // "allowSyntheticDefaultImports": true,  /* Allow default imports from modules with no default export. This does not affect code emit, just typechecking. */
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    "esModuleInterop": true                   /* Enables emit interoperability between CommonJS and ES Modules via creation of namespace objects for all imports. Implies 'allowSyntheticDefaultImports'. */
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    // "preserveSymlinks": true,              /* Do not resolve the real path of symlinks. */
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    /* Source Map Options */
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    // "sourceRoot": "",                      /* Specify the location where debugger should locate TypeScript files instead of source locations. */
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    // "mapRoot": "",                         /* Specify the location where debugger should locate map files instead of generated locations. */
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    // "inlineSourceMap": true,               /* Emit a single file with source maps instead of having a separate file. */
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    // "inlineSources": true,                 /* Emit the source alongside the sourcemaps within a single file; requires '--inlineSourceMap' or '--sourceMap' to be set. */
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    /* Experimental Options */
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    // "experimentalDecorators": true,        /* Enables experimental support for ES7 decorators. */
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    // "emitDecoratorMetadata": true,         /* Enables experimental support for emitting type metadata for decorators. */
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  }
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}

Setting Up Server

Installing Express

We need to install Express and Express Types so that Typescript can be type aware

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npm install express -s
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npm install @types/express -s

Building the Server

Now we can create a simple express server with the following file

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import express = require('express');
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// Create a new express application instance
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const app: express.Application = express();
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app.get('/', function (req, res) {
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  res.send('Hello World!');
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});
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app.listen(3000, function () {
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  console.log('Example app listening on port 3000!');
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});

Running the App

Compile the Application

The App must be compiled before it can be run, we do this with the following command

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npm run tsc

Which will place our app.ts file into the build folder

Run the Server

We can run the application by simply doing

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node .\build\app.js

And viewing the application at localhost:3000

Running without Transpiling

We can run the typescript directly without transpiling with the following

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npm install ts-node-dev -s

And by then adding the following to our package.json

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"scripts": {
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    "tsc": "tsc",
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    "dev": "ts-node-dev --respawn --transpileOnly ./app/app.ts",
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    "prod": "tsc && node ./build/app.js"
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},

We can run the dev server with

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npm run dev

And the production server with

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npm run prod