use a Set instead of a Map to store computed properties

lib/single-file/css-matched-rules.js

@@ -104,7 +104,7 @@ this.matchedRules = this.matchedRules || (() => {
 				} else if (cssRule.type == "Rule" && cssRule.prelude.children) {
 					const selectors = cssRule.prelude.children.toArray();
 					const selectorsText = cssRule.prelude.children.toArray().map(selector => cssTree.generate(selector));
-					const ruleInfo = { cssRule, mediaInfo, ruleIndex, sheetIndex, matchedSelectors: new Set(), declarations: new Map(), selectors, selectorsText };
+					const ruleInfo = { cssRule, mediaInfo, ruleIndex, sheetIndex, matchedSelectors: new Set(), declarations: new Set(), selectors, selectorsText };
 					if (!invalidSelector(selectorsText.join(","), stylesheet)) {
 						for (let selector = cssRule.prelude.children.head, selectorIndex = 0; selector; selector = selector.next, selectorIndex++) {
 							const selectorText = selectorsText[selectorIndex];
@@ -214,7 +214,7 @@ this.matchedRules = this.matchedRules || (() => {
 		if (!elementInfo) {
 			elementInfo = [];
 			if (elementStyle) {
-				elementInfo.push({ styleInfo: { cssStyle: elementStyle, declarations: new Map() } });
+				elementInfo.push({ styleInfo: { cssStyle: elementStyle, declarations: new Set() } });
 			}
 			mediaInfo.elements.set(element, elementInfo);
 		}
@@ -254,9 +254,8 @@ this.matchedRules = this.matchedRules || (() => {
 						mediaAllInfo.matchedStyles.set(cssStyle, info);
 					}
 				}
-				const styleValue = info.declarations.get(property);
-				if (!styleValue) {
-					info.declarations.set(property, declarationsInfo.styleValue);
+				if (!info.declarations.has(property)) {
+					info.declarations.add(property);
 				}
 			}
 		}));
@@ -284,10 +283,9 @@ this.matchedRules = this.matchedRules || (() => {
 			const declarationData = declaration.data;
 			const declarationText = cssTree.generate(declarationData);
 			if (declarationData.type == "Declaration" && (declarationText.match(REGEXP_VENDOR_IDENTIFIER) || !processedProperties.has(declarationData.property)) && !invalidDeclaration(declarationText, stylesheet)) {
-				const styleValue = cssTree.generate(declarationData.value);
-				const elementStyleInfo = declarationsInfo.get(declarationData);
-				if (styleValue.trim() && (!elementStyleInfo || (declarationData.important && !elementStyleInfo.important))) {
-					declarationsInfo.set(declarationData, { selectorInfo, styleValue, important: declarationData.important });
+				const declarationInfo = declarationsInfo.get(declarationData);
+				if (!declarationInfo || (declarationData.important && !declarationInfo.important)) {
+					declarationsInfo.set(declarationData, { selectorInfo, important: declarationData.important });
 					processedProperties.add(declarationData.property);
 				}
 			}