0.4.4 • Published 3 years ago

regex-cache v0.4.4

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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 with npm:

$ npm install --save regex-cache


Wrap a function like this:

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:

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);


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:

# 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:

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.



Pull requests and stars are always welcome. For bugs and feature requests, please create an issue.



Building docs

(This project's readme.md is generated by verb, please don't edit the readme directly. Any changes to the readme must be made in the .verb.md readme template.)

To generate the readme, run the following command:

$ 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:

$ npm install && npm test


Jon Schlinkert


Copyright © 2017, Jon Schlinkert. Released under the MIT License.

This file was generated by verb-generate-readme, v0.6.0, on September 01, 2017.