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- # regex-cache [](https://www.npmjs.com/package/regex-cache) [](https://npmjs.org/package/regex-cache) [](https://npmjs.org/package/regex-cache) [](https://travis-ci.org/jonschlinkert/regex-cache) [](https://ci.appveyor.com/project/jonschlinkert/regex-cache)
- > Memoize the results of a call to the RegExp constructor, avoiding repetitious runtime compilation of the same string and options, resulting in surprising performance improvements.
- ## Install
- Install with [npm](https://www.npmjs.com/):
- ```sh
- $ npm install --save regex-cache
- ```
- * Read [what this does](#what-this-does).
- * See [the benchmarks](#benchmarks)
- ## Usage
- Wrap a function like this:
- ```js
- var cache = require('regex-cache');
- var someRegex = cache(require('some-regex-lib'));
- ```
- **Caching a regex**
- If you want to cache a regex after calling `new RegExp()`, or you're requiring a module that returns a regex, wrap it with a function first:
- ```js
- var cache = require('regex-cache');
- function yourRegex(str, opts) {
- // do stuff to str and opts
- return new RegExp(str, opts.flags);
- }
- var regex = cache(yourRegex);
- ```
- ## Recommendations
- ### Use this when...
- * **No options are passed** to the function that creates the regex. Regardless of how big or small the regex is, when zero options are passed, caching will be faster than not.
- * **A few options are passed**, and the values are primitives. The limited benchmarks I did show that caching is beneficial when up to 8 or 9 options are passed.
- ### Do not use this when...
- * **The values of options are not primitives**. When non-primitives must be compared for equality, the time to compare the options is most likely as long or longer than the time to just create a new regex.
- ### Example benchmarks
- Performance results, with and without regex-cache:
- ```bash
- # no args passed (defaults)
- with-cache x 8,699,231 ops/sec ±0.86% (93 runs sampled)
- without-cache x 2,777,551 ops/sec ±0.63% (95 runs sampled)
- # string and six options passed
- with-cache x 1,885,934 ops/sec ±0.80% (93 runs sampled)
- without-cache x 1,256,893 ops/sec ±0.65% (97 runs sampled)
- # string only
- with-cache x 7,723,256 ops/sec ±0.87% (92 runs sampled)
- without-cache x 2,303,060 ops/sec ±0.47% (99 runs sampled)
- # one option passed
- with-cache x 4,179,877 ops/sec ±0.53% (100 runs sampled)
- without-cache x 2,198,422 ops/sec ±0.47% (95 runs sampled)
- # two options passed
- with-cache x 3,256,222 ops/sec ±0.51% (99 runs sampled)
- without-cache x 2,121,401 ops/sec ±0.79% (97 runs sampled)
- # six options passed
- with-cache x 1,816,018 ops/sec ±1.08% (96 runs sampled)
- without-cache x 1,157,176 ops/sec ±0.53% (100 runs sampled)
- #
- # diminishing returns happen about here
- #
- # ten options passed
- with-cache x 1,210,598 ops/sec ±0.56% (92 runs sampled)
- without-cache x 1,665,588 ops/sec ±1.07% (100 runs sampled)
- # twelve options passed
- with-cache x 1,042,096 ops/sec ±0.68% (92 runs sampled)
- without-cache x 1,389,414 ops/sec ±0.68% (97 runs sampled)
- # twenty options passed
- with-cache x 661,125 ops/sec ±0.80% (93 runs sampled)
- without-cache x 1,208,757 ops/sec ±0.65% (97 runs sampled)
- #
- # when non-primitive values are compared
- #
- # single value on the options is an object
- with-cache x 1,398,313 ops/sec ±1.05% (95 runs sampled)
- without-cache x 2,228,281 ops/sec ±0.56% (99 runs sampled)
- ```
- ## Run benchmarks
- Install dev dependencies:
- ```bash
- npm i -d && npm run benchmarks
- ```
- ## What this does
- If you're using `new RegExp('foo')` instead of a regex literal, it's probably because you need to dyamically generate a regex based on user options or some other potentially changing factors.
- When your function creates a string based on user inputs and passes it to the `RegExp` constructor, regex-cache caches the results. The next time the function is called if the key of a cached regex matches the user input (or no input was given), the cached regex is returned, avoiding unnecessary runtime compilation.
- Using the RegExp constructor offers a lot of flexibility, but the runtime compilation comes at a price - it's slow. Not specifically because of the call to the RegExp constructor, but **because you have to build up the string before `new RegExp()` is even called**.
- ## About
- ### Contributing
- Pull requests and stars are always welcome. For bugs and feature requests, [please create an issue](../../issues/new).
- ### Contributors
- | **Commits** | **Contributor** |
- | --- | --- |
- | 31 | [jonschlinkert](https://github.com/jonschlinkert) |
- | 1 | [MartinKolarik](https://github.com/MartinKolarik) |
- ### Building docs
- _(This project's readme.md is generated by [verb](https://github.com/verbose/verb-generate-readme), please don't edit the readme directly. Any changes to the readme must be made in the [.verb.md](.verb.md) readme template.)_
- To generate the readme, run the following command:
- ```sh
- $ npm install -g verbose/verb#dev verb-generate-readme && verb
- ```
- ### Running tests
- Running and reviewing unit tests is a great way to get familiarized with a library and its API. You can install dependencies and run tests with the following command:
- ```sh
- $ npm install && npm test
- ```
- ### Author
- **Jon Schlinkert**
- * [github/jonschlinkert](https://github.com/jonschlinkert)
- * [twitter/jonschlinkert](https://twitter.com/jonschlinkert)
- ### License
- Copyright © 2017, [Jon Schlinkert](https://github.com/jonschlinkert).
- Released under the [MIT License](LICENSE).
- ***
- _This file was generated by [verb-generate-readme](https://github.com/verbose/verb-generate-readme), v0.6.0, on September 01, 2017._
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