Abstract

Teach the TypeScript compiler to emit JavaScript files that can be run natively in the browser using es2015 module syntax.

Motivation

Browsers now support loading modules natively, without needing to rely on bundlers. However, unlike in NodeJS, the browser cannot try a bunch of different paths to find a file, it must fetch the correct file in a single standard HTTP request on the first try. This means that when you do import { Foo } from './foo', the browser will try to fetch a file at the path http://my-domain/path/foo. Unless you configure your HTTP server to serve up JS files when no extension is provided, the web server will likely not find any file at that path because the actual file lives at http://my-domain/path/foo.js. One potential solution to this problem is to write your TS like import { Foo } from './foo.js'. TypeScript is clever enough that it will realize that you really meant foo.ts during compilation, and it will successfully find type information. However, ts-node is not clever enough to handle these faux paths so if you want a library that works in either ts-node or browser you are out of luck.

The hope is that eventually TypeScript will add support for appending the .js extension as a compiler option, but for the time being we'll have to do it ourself.

Usage

1. Install typescript, ttypescript, and this transformer into your project if you don't already have them.

   npm install --save-dev typescript
   npm install --save-dev ttypescript
   npm install --save-dev @evg656e/typescript-transformer-append-js-extension

2. Add the transformer to your es2015 module tsconfig-es.json (or whatever tsconfig.json you are using to build es2015 modules)

   // tsconfig-es.json
   {
   	"compilerOptions": {
   		"module": "es2015",
   		"plugins": [
   			{
   				"transform": "@evg656e/typescript-transformer-append-js-extension/output/index.js",
   				"after": true,
   			}
   		]
   	},
   }

3. Write some typescript with normal imports

   // foo.ts
   export function foo() { console.log('foo') }

   // index.ts
   import { foo } from './foo'
   foo()

4. Compile using ttsc

   npx ttsc --project tsconfig-es.json

Configuration

By default, only relative paths are transformed. You can force the transformation of absolute paths using forceInclude option, which accepts an array of strings of RegExp patterns, e.g.:

```json
// tsconfig-es.json
{
	"compilerOptions": {
		"module": "es2015",
		"plugins": [
			{
				"transform": "@evg656e/typescript-transformer-append-js-extension/output/index.js",
				"after": true,
				"forceInclude": [
					"^lodash/.*"
				],
			}
		]
	},
}
```

Additionaly you can specify forceExclude option, which specifies paths that should be skipped when resolving forceInclude option:

```json
// tsconfig-es.json
{
	"compilerOptions": {
		"module": "es2015",
		"plugins": [
			{
				"transform": "@evg656e/typescript-transformer-append-js-extension/output/index.js",
				"after": true,
				"forceInclude": [
					"^lodash/.*"
				],
				"forceExclude": [
					"^lodash/isRegExp$"
				]
			}
		]
	},
}
```