Core: refactor diff to do less slow mutations

src/core/utilities.js

@@ -43,18 +43,13 @@ export const performance = {
 
 // Returns a new Array with the elements that are in a but not in b
 export function diff (a, b) {
-  const result = a.slice();
-
-  for (let i = 0; i < result.length; i++) {
-    for (let j = 0; j < b.length; j++) {
-      if (result[i] === b[j]) {
-        result.splice(i, 1);
-        i--;
-        break;
-      }
+  return a.reduce((result, item) => {
+    if (!b.includes(item)) {
+      result.push(item);
     }
-  }
-  return result;
+
+    return result;
+  }, []);
 }
 
 /**