perf(postcss-normalize-positions): increase perf (#694)

packages/postcss-normalize-positions/src/index.js

@@ -17,78 +17,117 @@ const vertical = {
     top: '0',
 };
 
-function transform (decl) {
-    const values = valueParser(decl.value);
-    const args = getArguments(values);
+function transform (value) {
+    const parsed = valueParser(value);
+    const args = getArguments(parsed);
     const relevant = [];
+
     args.forEach(arg => {
         relevant.push({
             start: null,
             end: null,
         });
+
         arg.forEach((part, index) => {
             const isPosition = ~directions.indexOf(part.value.toLowerCase()) || unit(part.value);
             const len = relevant.length - 1;
+
             if (relevant[len].start === null && isPosition) {
                 relevant[len].start = index;
                 relevant[len].end = index;
+
                 return;
             }
+
             if (relevant[len].start !== null) {
                 if (part.type === 'space') {
                     return;
                 } else if (isPosition) {
                     relevant[len].end = index;
+
                     return;
                 }
+
                 return;
             }
         });
     });
+
     relevant.forEach((range, index) => {
         if (range.start === null) {
             return;
         }
+
         const position = args[index].slice(range.start, range.end + 1);
+
         if (position.length > 3) {
             return;
         }
+
         const firstValue = position[0].value.toLowerCase();
         const secondValue = position[2] && position[2].value
             ? position[2].value.toLowerCase()
             : null;
+
         if (position.length === 1 || secondValue === 'center') {
             if (secondValue) {
                 position[2].value = position[1].value = '';
             }
+
             const map = Object.assign({}, horizontal, {
                 center,
             });
+
             if (has(map, firstValue)) {
                 position[0].value = map[firstValue];
             }
+
             return;
         }
+
         if (firstValue === 'center' && ~directions.indexOf(secondValue)) {
             position[0].value = position[1].value = '';
+
             if (has(horizontal, secondValue)) {
                 position[2].value = horizontal[secondValue];
             }
+
             return;
         }
+
         if (has(horizontal, firstValue) && has(vertical, secondValue)) {
             position[0].value = horizontal[firstValue];
             position[2].value = vertical[secondValue];
+
             return;
         } else if (has(vertical, firstValue) && has(horizontal, secondValue)) {
             position[0].value = horizontal[secondValue];
             position[2].value = vertical[firstValue];
+
             return;
         }
     });
-    decl.value = values.toString();
+
+    return parsed.toString();
 }
 
 export default plugin('postcss-normalize-positions', () => {
-    return css => css.walkDecls(/^(background(-position)?|(-webkit-)?perspective-origin)$/i, transform);
+    return css => {
+        const cache = {};
+
+        css.walkDecls(/^(background(-position)?|(-webkit-)?perspective-origin)$/i, (decl) => {
+            const value = decl.value;
+
+            if (cache[value]) {
+                decl.value = cache[value];
+
+                return;
+            }
+
+            const result = transform(value);
+
+            decl.value = result;
+            cache[value] = result;
+        });
+    };
 });