initial implementation of removeUnusedStyles plugin

plugins/removeUnusedStyles.js

@@ -0,0 +1,121 @@
+'use strict';
+
+exports.type = 'full';
+
+exports.active = true;
+
+exports.description = 'removes unused styles from <style> based on usage data';
+
+exports.params = {
+    removeUnusedStyles: {
+        ids: true,
+        classes: true,
+        tags: true
+    }
+};
+
+var csso = require('csso');
+
+/**
+ * Remove unused styles from <style> based on usage data
+ *
+ * @author Roman Dvornov
+ */
+exports.fn = function(ast, params) {
+
+    var usageData = collectUsageData(ast);
+    var styles = findStyleElems(ast);
+
+    for (var key in usageData) {
+        if (!shouldFilter(params, key)) {
+            usageData[key] = false;
+        }
+    }
+
+    styles.forEach(function(style) {
+        var styleCss = style.content[0].text || style.content[0].cdata || [];
+        var DATA = styleCss.indexOf('>') >= 0 || styleCss.indexOf('<') >= 0 ? 'cdata' : 'text';
+
+        style.content[0][DATA] = csso.minify(styleCss, {
+            usage: usageData
+        }).css;
+    });
+
+    return ast;
+};
+
+function shouldFilter(params, name) {
+    if (!params || 'removeUnusedStyles' in params === false) {
+        return true;
+    }
+
+    if (params.removeUnusedStyles && name in params.removeUnusedStyles === false) {
+        return true;
+    }
+
+    return Boolean(params.removeUnusedStyles && params.removeUnusedStyles[name]);
+}
+
+function findStyleElems(ast) {
+
+    function walk(items, styles) {
+        for (var i = 0; i < items.content.length; i++) {
+            var item = items.content[i];
+
+            // go deeper
+            if (item.content) {
+                walk(item, styles);
+            }
+
+            if (item.isElem('style') && !item.isEmpty()) {
+                styles.push(item);
+            }
+        }
+
+        return styles;
+    }
+
+    return walk(ast, []);
+}
+
+function collectUsageData(ast) {
+
+    function walk(items, usageData) {
+        for (var i = 0; i < items.content.length; i++) {
+            var item = items.content[i];
+
+            // go deeper
+            if (item.content) {
+                walk(item, usageData);
+            }
+
+            if (item.isElem()) {
+                usageData.tags[item.elem] = true;
+
+                if (item.hasAttr('id')) {
+                    usageData.ids[item.attr('id').value] = true;
+                }
+
+                if (item.hasAttr('class')) {
+                    item.attr('class').value.replace(/^\s+|\s+$/g, '').split(/\s+/).forEach(function(className) {
+                        usageData.classes[className] = true;
+                    });
+                }
+            }
+        }
+
+        return usageData;
+    }
+
+    var usageData = walk(ast, {
+        ids: Object.create(null),
+        classes: Object.create(null),
+        tags: Object.create(null)
+    });
+
+    for (var key in usageData) {
+        usageData[key] = Object.keys(usageData[key]);
+    }
+
+    return usageData;
+}