1 files changed, 38 insertions, 0 deletions
diff --git a/browser/components/newtab/common/Dedupe.jsm b/browser/components/newtab/common/Dedupe.jsm
new file mode 100644
index 0000000000..280615ba6a
--- /dev/null
+++ b/browser/components/newtab/common/Dedupe.jsm
@@ -0,0 +1,38 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+this.Dedupe = class Dedupe {
+  constructor(createKey) {
+    this.createKey = createKey || this.defaultCreateKey;
+  }
+
+  defaultCreateKey(item) {
+    return item;
+  }
+
+  /**
+   * Dedupe any number of grouped elements favoring those from earlier groups.
+   *
+   * @param {Array} groups Contains an arbitrary number of arrays of elements.
+   * @returns {Array} A matching array of each provided group deduped.
+   */
+  group(...groups) {
+    const globalKeys = new Set();
+    const result = [];
+    for (const values of groups) {
+      const valueMap = new Map();
+      for (const value of values) {
+        const key = this.createKey(value);
+        if (!globalKeys.has(key) && !valueMap.has(key)) {
+          valueMap.set(key, value);
+        }
+      }
+      result.push(valueMap);
+      valueMap.forEach((value, key) => globalKeys.add(key));
+    }
+    return result.map(m => Array.from(m.values()));
+  }
+};
+
+const EXPORTED_SYMBOLS = ["Dedupe"];