> 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).
_(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:
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:
