# resolve-package-path [![CI](https://github.com/stefanpenner/resolve-package-path/workflows/CI/badge.svg)](https://github.com/stefanpenner/resolve-package-path/actions/workflows/ci.yml)

This project is special-purpose, made to resolve `package.json` files for:

  - a given module name and basedir or
  - a given basedir

It cannot and does not resolve anything else.

To achieve its file-resolution performance, it does two specific things:

- It memoizes results identically to node's `require`. Specifically,
  for a given moduleName and baseDir it will, for the duration of the process,
  always return the exact same response.

- It re-implements the parts of `require.resolve` needed to resolve package.json
  files ONLY. This removes unneeded I/O. (based on @davecombs approach)

## Usage

```sh
yarn add resolve-package-path
```

```js
const resolvePackagePath = require('resolve-package-path');

resolvePackagePath('rsvp', 'base-dir/to/start/the/node_resolution-algorithm-from') // => /path/to/rsvp.json or null

const { findUpPackagePath } = resolvePackagePath;
findUpPackagePath('base-dir/to/start') // => path/to/package.json or null
```

## Advanced usage

### Preserve Symlinks

Node supports `--preserve-symlinks` and `NODE_PRESERVE_SYMLINKS=1` for compatibility this library respects these.

### Disable default caching

Although by default `resolve-package-path` caches or memoizes results, this feature can be disabled:

```js
const resolvePackagePath = require('resolve-package-path');

resolvePackagePath('rsvp', 'base-dir/to/start/the/node_resolution-algorithm-from', false) // => uncached result /path/to/rsvp.json or null

const { findUpPackagePath } = resolvePackagePath;
findUpPackagePath('base-dir/to/start', false) // => path/to/package.json or null
```

### Purge the cache

```js
const resolvePackagePath = require('resolve-package-path');
resolvePackagePath._resetCache();
```

### Provide an alternative cache

In some advanced circumtances, you may want to gain access to the cache to share between more systems.
In that case, a cache instance of the following form can be provided as a third argument:

```js
cache = {
  RESOLVED_PACKAGE_PATH: new Map(),
  REAL_FILE_PATH: new Map(),
  REAL_DIRECTORY_PATH: new Map(),
};
findUpCache = new Map();

const resolvePackagePath = require('resolve-package-path');
resolvePackagePath('rsvp', 'path/to/start/from', cache);

const { findUpPackagePath } = resolvePackagePath;
findUpPackagePath('base-dir/to/start', findUpCache) // => path/to/package.json or null
```

### Use internal helper functions

For consumers who also do `getRealFilePath` or
`getRealDirectoryPath` calls on relevant paths, we expose them as utilities.
These utilties ensure identical functionality to resolve-package-path, and a
shared cache, which may help reduce IO.