keep(sel) -> shouldDrop(sel) & show logging of removed selectors

Author: leeoniya

README.md

@@ -17,7 +17,7 @@ The entire logic for DropCSS is this [~60 line file](https://github.com/leeoniya
 ### Install
 
 ```
-npm install --save-dev dropcss
+npm install -D dropcss
 ```
 
 ---
@@ -45,17 +45,28 @@ let css = `
     }
 `;
 
+const whitelist = /\b(?:#foo|\.bar)\b/;
+
+let dropped = new Set();
+
 let cleansedCSS = dropcss({
     html,
     css,
-    keep: (sel) => {
-        // test selector against some whitelist
-        // and return `true` to retain it
-        return /#foo/.test(sel);
+    shouldDrop: (sel) => {
+        if (whitelist.test(sel))
+            return false;
+        else {
+            dropped.add(sel);
+            return true;
+        }
     },
 })
 ```
 
+`shouldDrop` is called for every CSS selector that could not be matched in the `html`.
+Return `false` to retain it or `true` to drop it.
+Additionally, this callback can be used to log all removed selectors.
+
 ---
 ### Features
 

package.json

@@ -1,6 +1,6 @@
 {
   "name": "dropcss",
-  "version": "0.1.0",
+  "version": "0.2.0",
   "description": "Unused CSS Cleaner",
   "main": "./src/dropcss.js",
   "scripts": {

src/dropcss.js

@@ -6,6 +6,8 @@ const adapter = require("./adapter");
 // https://developer.mozilla.org/en-US/docs/Web/CSS/pseudo-classes
 const pseudoClassNonTransient = /:(?:first|last|nth|only|not|empty)\b/;		// |lang
 
+const doDrop = sel => true;
+
 function dropcss(opts) {
 	const htmlAst = parse(opts.html);
 
@@ -15,7 +17,7 @@ function dropcss(opts) {
 		parseAtrulePrelude: false
 	});
 
-	const keep = opts.keep || (() => false);
+	const shouldDrop = opts.shouldDrop || doDrop;
 
 	csstree.walk(cssAst, function(node, item, list) {
 		if (node.type == "Rule") {
@@ -33,7 +35,7 @@ function dropcss(opts) {
 				// remove any empty leftovers eg :not() - [tabindex="-1"]:focus:not(:focus-visible)
 				.replace(/:[a-z-]+\(\)/gm, '');
 
-				if (domSel == '' || CSSselect.selectOne(domSel, htmlAst.childNodes, {adapter}) || keep(sel))
+				if (domSel == '' || CSSselect.selectOne(domSel, htmlAst.childNodes, {adapter}) || shouldDrop(sel) !== true)
 					pre.push(sel);
 			});