Refactor border property retrieval logic

Introduced getBorderItem to centralize and simplify retrieval of border property items in prepareBorderProperties. This reduces code duplication and improves maintainability.

Author: asamuzaK

lib/normalize.js

@@ -112,6 +112,23 @@ const getPropertyItem = (property, properties) => {
   return propertyItem;
 };
 
+/**
+ * Retrieves a property item from borderItems, properties, or creates a new one.
+ * Prioritizes borderItems (processed items) over properties (existing items).
+ *
+ * @param {string} property - The name of the property.
+ * @param {Map} borderItems - The map containing processed border items.
+ * @param {Map} properties - The map containing all properties.
+ * @returns {Object} The property item.
+ */
+const getBorderItem = (property, borderItems, properties) => {
+  return (
+    borderItems.get(property) ??
+    properties.get(property) ??
+    createPropertyItem(property)
+  );
+};
+
 /**
  * Calculates the value for a specific position (top, right, bottom, left)
  * based on the array of values provided for a shorthand property.
@@ -1030,29 +1047,20 @@ const prepareBorderProperties = (property, value, priority, properties, opt = {}
   const borderProps = new Map([[BORDER, borderItems.get(BORDER)]]);
   for (const line of borderLines) {
     const lineProperty = `${BORDER}-${line}`;
-    const lineItem =
-      borderItems.get(lineProperty) ??
-      properties.get(lineProperty) ??
-      createPropertyItem(lineProperty);
+    const lineItem = getBorderItem(lineProperty, borderItems, properties);
     borderProps.set(lineProperty, lineItem);
   }
   for (const position of borderPositions) {
     const positionProperty = `${BORDER}-${position}`;
-    const positionItem =
-      borderItems.get(positionProperty) ??
-      properties.get(positionProperty) ??
-      createPropertyItem(positionProperty);
+    const positionItem = getBorderItem(positionProperty, borderItems, properties);
     borderProps.set(positionProperty, positionItem);
     for (const line of borderLines) {
       const longhandProperty = `${BORDER}-${position}-${line}`;
-      const longhandItem =
-        borderItems.get(longhandProperty) ??
-        properties.get(longhandProperty) ??
-        createPropertyItem(longhandProperty);
+      const longhandItem = getBorderItem(longhandProperty, borderItems, properties);
       borderProps.set(longhandProperty, longhandItem);
     }
   }
-  const borderImageItem = borderItems.get(BORDER_IMAGE) ?? createPropertyItem(BORDER_IMAGE);
+  const borderImageItem = getBorderItem(BORDER_IMAGE, borderItems, properties);
   borderProps.set(BORDER_IMAGE, borderImageItem);
   return borderProps;
 };