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node_modules/fast-equals/recipes/non-standard-properties.md

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+# Non-standard properties
+
+Sometimes, objects require a comparison that extend beyond its own keys, or even its own properties or symbols. Using a custom object comparator with `createCustomEqual` allows these kinds of comparisons.
+
+```ts
+import { createCustomEqual } from 'fast-equals';
+import type { TypeEqualityComparator } from 'fast-equals';
+
+type AreObjectsEqual = TypeEqualityComparator<Record<any, any>, undefined>;
+
+class HiddenProperty {
+  visible: boolean;
+  #hidden: string;
+
+  constructor(value: string) {
+    this.visible = true;
+    this.#hidden = value;
+  }
+
+  get hidden() {
+    return this.#hidden;
+  }
+}
+
+function createAreObjectsEqual(
+  areObjectsEqual: AreObjectsEqual,
+): AreObjectsEqual {
+  return function (a, b, state) {
+    if (!areObjectsEqual(a, b, state)) {
+      return false;
+    }
+
+    const aInstance = a instanceof HiddenProperty;
+    const bInstance = b instanceof HiddenProperty;
+
+    if (aInstance || bInstance) {
+      return aInstance && bInstance && a.hidden === b.hidden;
+    }
+
+    return true;
+  };
+}
+
+const deepEqual = createCustomEqual({
+  createCustomConfig: ({ areObjectsEqual }) =>
+    createAreObjectsEqual(areObjectsEqual),
+});
+```