caching-transform

What is caching-transform?

The caching-transform npm package is designed to cache the results of expensive transformation operations, such as those performed during the build or compilation process. It works by storing the results of these operations in a cache, keyed by a hash of the input. This means that if the input hasn't changed, the transformation can be skipped, and the cached result can be used instead. This can significantly speed up build times in development environments or for repeated builds.

What are caching-transform's main functionalities?

Caching file transformations

This code demonstrates how to use caching-transform to cache the results of a file transformation. The `transform` function represents an expensive operation. The `cache` function, created by `cachingTransform`, checks if a cached result exists for the given input. If not, it runs the transformation and caches the result.

const cachingTransform = require('caching-transform');
const fs = require('fs');
const path = require('path');

const cacheDir = path.join(__dirname, '.cache');

const transform = (input) => {
  // Perform an expensive transformation here
  return transformedInput;
};

const cache = cachingTransform({
  cacheDir: cacheDir,
  transform: transform
});

const input = fs.readFileSync('input.txt', 'utf8');
const output = cache(input);
console.log(output);

Other packages similar to caching-transform

babel-loader

babel-loader is a Webpack plugin that transpiles JavaScript files using Babel and caches the results. While caching-transform is a more generic tool that can be used with any transformation function, babel-loader is specifically designed for use with Webpack and Babel.

cache-loader

cache-loader is another Webpack loader that caches the result of expensive operations. It is similar to caching-transform in its purpose of caching transformation results to speed up build processes. However, cache-loader is specifically tailored for Webpack's ecosystem.

hard-source-webpack-plugin

hard-source-webpack-plugin is a plugin for Webpack that provides an intermediate caching step for modules. Like caching-transform, it aims to speed up build times by caching the results of expensive operations. However, it is tightly integrated with Webpack's architecture and caching strategy.

README

caching-transform

Wraps a transform and provides caching.

Caching transform results can greatly improve performance. nyc saw dramatic performance increases when we implemented caching.

Install

$ npm install caching-transform

Usage

const cachingTransform = require('caching-transform');

const transform = cachingTransform({
	cacheDir: '/path/to/cache/directory',
	salt: 'hash-salt',
	transform: (input, metadata, hash) => {
		// ... Expensive operations ...
		return transformedResult;
	}
});

transform('some input for transpilation')
// => fetch from the cache,
//    or run the transform and save to the cache if not found there

API

cachingTransform(options)

Returns a transform callback that takes two arguments:

• input a string to be transformed
• metadata an arbitrary data object

Both arguments are passed to the wrapped transform. Results are cached in the cache directory using an sha256 hash of input and an optional salt value. If a cache entry already exist for input, the wrapped transform function will never be called.

options

salt

Type: string Buffer
Default: ''

A value that uniquely identifies your transform:

const pkg = require('my-transform/package.json');
const salt = pkg.name + ':' + pkg.version;

Including the version in the salt ensures existing cache entries will be automatically invalidated when you bump the version of your transform. If your transform relies on additional dependencies, and the transform output might change as those dependencies update, then your salt should incorporate the versions of those dependencies as well.

transform

Type: Function(input: string|Buffer, metadata: *, hash: string): string|Buffer

• input: The value to be transformed. It is passed through from the wrapper.
• metadata: An arbitrary data object passed through from the wrapper. A typical value might be a string filename.
• hash: The salted hash of input. Useful if you intend to create additional cache entries beyond the transform result (i.e. nyc also creates cache entries for source-map data). This value is not available if the cache is disabled, if you still need it, the default can be computed via hasha([input, salt]).

The transform function will return a string (or Buffer if encoding === 'buffer') containing the result of transforming input.

factory

Type: Function(cacheDir: string): transformFunction

If the transform function is expensive to create, and it is reasonable to expect that it may never be called during the life of the process, you may supply a factory function that will be used to create the transform function the first time it is needed.

A typical usage would be to prevent eagerly requireing expensive dependencies like Babel:

function factory() {
	// Using the factory function, you can avoid loading Babel until you are sure it is needed.
	const babel = require('babel-core');

	return (code, metadata) => {
		return babel.transform(code, {filename: metadata.filename, plugins: [/* ... */]});
	};
}

cacheDir

Required unless caching is disabled
Type: string

The directory where cached transform results will be stored. The directory is automatically created with mkdirp. You can set options.createCacheDir = false if you are certain the directory already exists.

ext

Type: string
Default: ''

An extension that will be appended to the salted hash to create the filename inside your cache directory. It is not required, but recommended if you know the file type. Appending the extension allows you to easily inspect the contents of the cache directory with your file browser.

shouldTransform

Type: Function(input: string|Buffer, additionalData: *)
Default: Always transform

A function that examines input and metadata to determine whether the transform should be applied. Returning false means the transform will not be applied and input will be returned unmodified.

disableCache

Type: boolean
Default: false

If true, the cache is ignored and the transform is used every time regardless of cache contents.

hashData

Type: Function(input: string|Buffer, metadata: *): string|Buffer|Array[string|Buffer]

Provide additional data that should be included in the hash.

One potential use is including the metadata in the hash by coercing it to a hashable string or buffer:

function hashData(input, metadata) {
	return JSON.stringify(metadata);
}

(Note that metadata is not taken into account otherwise.)

filenamePrefix

Type: Function(metadata: *): string

Provide a filename to prefix the cache entry. The return value may not contain any path separators.

function filenamePrefix(metadata) {
	return path.parse(metadata.filename || '').name + '-';
}

onHash

Type: Function(input: string|Buffer, metadata: *, hash: string)

Function that is called after input is hashed.

encoding

Type: string
Default: 'utf8'

The encoding to use when writing to / reading from the filesystem. If set it to buffer, then buffers will be returned from the cache instead of strings.

License

MIT © James Talmage