Incorrect Brotli example

[matthewdouglas]

Documentation Is:

• Missing
• Needed
• Confusing
• Not Sure?

Please Explain in Detail...

The Brotli examples in the README do not correctly set the compressionOptions. The BROTLI_PARAM_QUALITY parameter is the equivalent to zlib's level option in terms of functionality, but not naming.

Your Proposal for Changes

1. Revise the examples to set the Brotli parameters correctly.

const zlib = require('zlib');
...
compressionOptions: {
  params: {
    [zlib.constants.BROTLI_PARAM_QUALITY]: 11
  }
}

2. Update the note to be more clear about BROTLI_PARAM_QUALITY being functionally equivalent to level, but not syntactically.

3. Update note regarding Node version as Brotli native support was backported to Node 10.16.

[alexander-akait]

Feel free to send a PR with fixes

[180254]

Points 1 and 2 described there are still valid and documentation needs to be revised.

Rationale:

• In the typescript declaration for node zlib module (https://unpkg.com/browse/@types/node@14.14.2/zlib.d.ts) ZlibOptions interface has the "level" property, while BrotliOptions does not.
• In the zlib module source code (https://github.com/nodejs/node/blob/v15.0.1/lib/zlib.js) Brotli (line 793) do not handle the "level" property.
• This plug-in (compression-webpack-plugin) has no additional conditions in the code to support this syntax.
• I created reproduction-steps (https://github.com/180254/compression-webpack-plugin-issue-154) that shows that master-branch-example does not work. I compressed a file several times. Changing "level" has no effect, while changing BROTLI_PARAM_QUALITY has.

89930 bytes - jquery.js
28094 bytes - jquery.js-compressionOptions-level-0.br
28094 bytes - jquery.js-compressionOptions-level-11.br
37188 bytes - jquery.js-compressionOptions-params-BROTLI_PARAM_QUALITY-0.br
28094 bytes - jquery.js-compressionOptions-params-BROTLI_PARAM_QUALITY-11.br

[alexander-akait]

Feel free to open a new issue or send a fix