perf(postcss-normalize-display-values): increase perf (#695)

packages/postcss-normalize-display-values/src/index.js

@@ -1,25 +1,49 @@
-import postcss from 'postcss';
-import valueParser from 'postcss-value-parser';
-import getMatchFactory from 'lerna:cssnano-util-get-match';
-import mappings from './lib/map';
+import postcss from "postcss";
+import valueParser from "postcss-value-parser";
+import getMatchFactory from "lerna:cssnano-util-get-match";
+import mappings from "./lib/map";
 
 const getMatch = getMatchFactory(mappings);
 
 function evenValues (list, index) {
     return index % 2 === 0;
 }
 
-function transform (node) {
-    const {nodes} = valueParser(node.value);
-    if (nodes.length === 1) {
-        return;
-    }
-    const match = getMatch(nodes.filter(evenValues).map(n => n.value.toLowerCase()));
-    if (match) {
-        node.value = match;
-    }
-}
+export default postcss.plugin("postcss-normalize-display-values", () => {
+    return css => {
+        const cache = {};
+
+        css.walkDecls(/display/i, decl => {
+            const value = decl.value;
+
+            if (cache[value]) {
+                decl.value = cache[value];
+
+                return;
+            }
+
+            const {nodes} = valueParser(value);
+
+            if (nodes.length === 1) {
+                cache[value] = value;
+
+                return;
+            }
+
+            const match = getMatch(
+                nodes.filter(evenValues).map(n => n.value.toLowerCase())
+            );
+
+            if (!match) {
+                cache[value] = value;
+
+                return;
+            }
+
+            const result = match;
 
-export default postcss.plugin('postcss-normalize-display-values', () => {
-    return css => css.walkDecls(/display/i, transform);
+            decl.value = result;
+            cache[value] = result;
+        });
+    };
 });