Missing number in Js

Algorithms/MissingNumbers/Javascript/ravaria/problem.js

+function getFrecuency(arr) {
+  return arr.reduce((acc, ele) => {
+      if (acc.has(ele)) {
+          const i = acc.get(ele);
+          acc.set(ele, i + 1);
+      } else {
+          acc.set(ele, 1);
+      }
+      return acc;
+  }, new Map());
+} 
+
+// Complete the missingNumbers function below.
+function missingNumbers(arr, brr) {
+  const result = [];
+  const arrF = getFrecuency(arr);
+  const brrF = getFrecuency(brr);
+  for ( let  value of brrF.keys()) {
+      if ( arrF.has(value)) {
+          if ( arrF.get(value) != brrF.get(value)) {
+              result.push(value);
+          }
+      } else {
+          result.push(value);
+      }
+  }
+  return result.sort(function(a, b) { return a - b; });
+}
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