feat: Add minify option like js-reader (#35)

* Update package-lock.json

* add needed deps

* implement cssnano and autoprefixer on the css feed

* add tests and docs

* elaborate on the api docs

* add snapshot test to reduce ambiguity on minify test

Author: stipsan

README.md

@@ -85,7 +85,19 @@ Example
 const bundle = await cssReader([feed, ...feeds])
 ```
 
-Returns: `Promise<string>` - A promise that resolves to a bundle string.
+This module has the following API:
+
+### function(feeds, [options])
+
+Supported arguments are:
+
+* `feeds` - Array - An Array of feeds.
+* `options` - Object - configuration.
+    * `options.minify` (default: false) Specify whether to minify code using [cssnano](https://cssnano.co/).
+
+Returns: `Promise<string>` - A promise that resolves to a bundle string that is processed by [autoprefixer](https://github.com/postcss/autoprefixer).
+
+Remember to specify a [browserslist](https://github.com/browserslist/browserslist) in your project to ensure cssnano and autoprefixer support the browsers your users use.
 
 ## Contributing
 

lib/reader.js

@@ -2,8 +2,11 @@
 
 const assert = require('assert');
 const { EOL } = require('os');
+const postcss = require('postcss');
+const autoprefixer = require('autoprefixer');
+const cssnano = require('cssnano');
 
-module.exports = async function reader(feeds = []) {
+module.exports = async function reader(feeds = [], options = {}) {
     assert(
         feeds.length,
         `Expected at least 1 feed to be given. Instead got "${feeds.length}"`
@@ -15,6 +18,11 @@ module.exports = async function reader(feeds = []) {
 
     feeds = [].concat(...feeds);
 
+    const opts = {
+        minify: false,
+        ...options,
+    };
+
     const feedMap = new Map();
     feeds.forEach(feed => {
         // because feedMap preserves order, when we get a duplicate we actually
@@ -25,7 +33,17 @@ module.exports = async function reader(feeds = []) {
     });
 
     // backwards compatible refactor to `.source` from `.content`
-    return Array.from(feedMap.values())
+    const precss = Array.from(feedMap.values())
         .map(feed => (feed.source || feed.content).trim())
         .join(EOL + EOL);
+
+    const processor = postcss(autoprefixer());
+
+    if (opts.minify) {
+        processor.use(cssnano());
+    }
+
+    const { css } = await processor.process(precss, { map: false });
+
+    return css;
 };