npm package: @novo-learning/tsconfig-paths
Description: Load node modules according to tsconfig paths, in run-time or via API.
Author: Jonas Kello
Latest version: 3.10.0

# tsconfig-paths

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[![MIT license][license-image]][license-url]
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Use this to load modules whose location is specified in the `paths` section of `tsconfig.json`. Both loading at run-time and via API are supported.

Typescript by default mimics the Node.js runtime resolution strategy of modules. But it also allows the use of [path mapping](https://www.typescriptlang.org/docs/handbook/module-resolution.html) which allows arbitrary module paths (that doesn't start with "/" or ".") to be specified and mapped to physical paths in the filesystem. The typescript compiler can resolve these paths from `tsconfig` so it will compile OK. But if you then try to execute the compiled files with node (or ts-node), it will only look in the `node_modules` folders all the way up to the root of the filesystem and thus will not find the modules specified by `paths` in `tsconfig`.

If you require this package's `tsconfig-paths/register` module it will read the `paths` from `tsconfig.json` and convert node's module loading calls into to physcial file paths that node can load.

## How to install

```
yarn add --dev tsconfig-paths
```

or

```
npm install --save-dev tsconfig-paths
```

## How to use

### With node

`node -r tsconfig-paths/register main.js`

### With ts-node

`ts-node -r tsconfig-paths/register main.ts`

If `process.env.TS_NODE_PROJECT` is set it will be used to resolved tsconfig.json

### With webpack

For webpack please use the [tsconfig-paths-webpack-plugin](https://github.com/dividab/tsconfig-paths-webpack-plugin).

### With mocha and ts-node

As of Mocha >= 4.0.0 the `--compiler` was [deprecated](https://github.com/mochajs/mocha/wiki/compilers-deprecation). Instead `--require` should be used. You also have to specify a glob that includes `.ts` files because mocha looks after files with `.js` extension by default.

```bash
mocha -r ts-node/register -r tsconfig-paths/register "test/**/*.ts"
```

### With other commands

As long as the command has something similar to a `--require` option that can load a module before it starts, tsconfig-paths should be able to work with it.

## Bootstrapping with explicit params

If you want more granular control over tsconfig-paths you can bootstrap it. This can be useful if you for instance have compiled with `tsc` to another directory where `tsconfig.json` doesn't exists.

```javascript
const tsConfig = require("./tsconfig.json");
const tsConfigPaths = require("tsconfig-paths");

const baseUrl = "./"; // Either absolute or relative path. If relative it's resolved to current working directory.
const cleanup = tsConfigPaths.register({
  baseUrl,
  paths: tsConfig.compilerOptions.paths
});

// When path registration is no longer needed
cleanup();
```

Then run with:

`node -r ./tsconfig-paths-bootstrap.js main.js`

## Configuration Options

You can set options by passing them before the script path, via programmatic usage or via environment variables.

```bash
ts-node --project customLocation/tsconfig.json -r tsconfig-paths/register "test/**/*.ts"
```

### CLI and Programmatic Options

_Environment variable denoted in parentheses._

- `-P, --project [path]` Path to TypeScript JSON project file (`TS_NODE_PROJECT`)

## Config loading process

1.  Use explicit params passed to register
2.  Use `process.env.TS_NODE_PROJECT` to resolve tsConfig.json and the specified baseUrl and paths.
3.  Resolves tsconfig.json from current working directory and the specified baseUrl and paths.

## Programmatic use

The public API consists of these functions:

- [register](#register)
- [loadConfig](#loadConfig)
- [createMatchPath](#createMatchPath) / [createMatchPathAsync](#createMatchPathAsync)
- [matchFromAbsolutePaths](#matchFromAbsolutePaths) / [matchFromAbsolutePathsAsync](#matchFromAbsolutePathsAsync)

### register

```typescript
export interface ExplicitParams {
  baseUrl: string;
  paths: { [key: string]: Array<string> };
  mainFields?: Array<string>;
  addMatchAll?: boolean;
}

/**
 * Installs a custom module load function that can adhere to paths in tsconfig.
 */
export function register(explicitParams: ExplicitParams): () => void;
```

This function will patch the node's module loading so it will look for modules in paths specified by tsconfig.json.
A function is returned for you to reinstate Node's original module loading.

### loadConfig

```typescript
export function loadConfig(cwd: string = process.cwd()): ConfigLoaderResult;

export type ConfigLoaderResult =
  | ConfigLoaderSuccessResult
  | ConfigLoaderFailResult;

export interface ConfigLoaderSuccessResult {
  resultType: "success";
  absoluteBaseUrl: string;
  paths: { [key: string]: Array<string> };
}

export interface ConfigLoaderFailResult {
  resultType: "failed";
  message: string;
}
```

This function loads the tsconfig.json. It will start searching from the specified `cwd` directory. Passing the tsconfig.json file directly instead of a directory also works.

### createMatchPath

```typescript
/**
 * Function that can match a path
 */
export interface MatchPath {
  (
    requestedModule: string,
    readJson?: Filesystem.ReadJsonSync,
    fileExists?: (name: string) => boolean,
    extensions?: ReadonlyArray<string>
  ): string | undefined;
}

/**
 * Creates a function that can resolve paths according to tsconfig paths property.
 * @param absoluteBaseUrl Absolute version of baseUrl as specified in tsconfig.
 * @param paths The paths as specified in tsconfig.
 * @param mainFields A list of package.json field names to try when resolving module files.
 * @param addMatchAll Add a match-all "*" rule if none is present
 * @returns a function that can resolve paths.
 */
export function createMatchPath(
  absoluteBaseUrl: string,
  paths: { [key: string]: Array<string> },
  mainFields: string[] = ["main"],
  addMatchAll: boolean = true
): MatchPath {
```

The `createMatchPath` function will create a function that can match paths. It accepts `baseUrl` and `paths` directly as they are specified in tsconfig and will handle resolving paths to absolute form. The created function has the signare specified by the type `MatchPath` above.

### matchFromAbsolutePaths

```typescript
/**
 * Finds a path from tsconfig that matches a module load request.
 * @param absolutePathMappings The paths to try as specified in tsconfig but resolved to absolute form.
 * @param requestedModule The required module name.
 * @param readJson Function that can read json from a path (useful for testing).
 * @param fileExists Function that checks for existance of a file at a path (useful for testing).
 * @param extensions File extensions to probe for (useful for testing).
 * @param mainFields A list of package.json field names to try when resolving module files.
 * @returns the found path, or undefined if no path was found.
 */
export function matchFromAbsolutePaths(
  absolutePathMappings: ReadonlyArray<MappingEntry.MappingEntry>,
  requestedModule: string,
  readJson: Filesystem.ReadJsonSync = Filesystem.readJsonFromDiskSync,
  fileExists: Filesystem.FileExistsSync = Filesystem.fileExistsSync,
  extensions: Array<string> = Object.keys(require.extensions),
  mainFields: string[] = ["main"]
): string | undefined {
```

This function is lower level and requries that the paths as already been resolved to absolute form and sorted in correct order into an array.

### createMatchPathAsync

This is the async version of `createMatchPath`. It has the same signature but with a callback parameter for the result.

### matchFromAbsolutePathsAsync

This is the async version of `matchFromAbsolutePaths`. It has the same signature but with a callback parameter for the result.

## How to publish

```
yarn version --patch
yarn version --minor
yarn version --major
```

[version-image]: https://img.shields.io/npm/v/tsconfig-paths.svg?style=flat
[version-url]: https://www.npmjs.com/package/tsconfig-paths
[travis-image]: https://travis-ci.com/dividab/tsconfig-paths.svg?branch=master&style=flat
[travis-url]: https://travis-ci.com/dividab/tsconfig-paths
[codecov-image]: https://codecov.io/gh/dividab/tsconfig-paths/branch/master/graph/badge.svg
[codecov-url]: https://codecov.io/gh/dividab/tsconfig-paths
[license-image]: https://img.shields.io/github/license/dividab/tsconfig-paths.svg?style=flat
[license-url]: https://opensource.org/licenses/MIT
[prettier-image]: https://img.shields.io/badge/code_style-prettier-ff69b4.svg
[prettier-url]: https://github.com/prettier/prettier