diff --git a/snippets/unionBy.md b/snippets/unionBy.md
new file mode 100644
index 000000000..3680c6d1c
--- /dev/null
+++ b/snippets/unionBy.md
@@ -0,0 +1,18 @@
+### unionBy
+
+Returns every element that exists in any of the two arrays once, after applying the provided function to each array element of both.
+
+Create a `Set` by applying all `fn` to all values of `a`.
+Create a `Set` from `a` and all elements in `b` whose value, after applying `fn` does not match a value in the previously created set.
+Return the last set converted to an array.
+
+```js
+const unionBy = (a, b, fn) => {
+  const s = new Set(a.map(v => fn(v)));
+  return Array.from(new Set([...a, ...b.filter(x => !s.has(fn(x)))]));
+};
+```
+
+```js
+unionBy([2.1], [1.2, 2.3], Math.floor); // [2.1, 1.2]
+```
diff --git a/snippets/unionWith.md b/snippets/unionWith.md
new file mode 100644
index 000000000..dbfee938b
--- /dev/null
+++ b/snippets/unionWith.md
@@ -0,0 +1,16 @@
+### unionWith
+
+Returns every element that exists in any of the two arrays once, using a provided comparator function.
+
+Create a `Set` with all values of `a` and values in `b` for which the comparator finds no matches in `a`, using `Array.findIndex()`.
+
+```js
+const unionWith = (a, b, comp) =>
+  Array.from(
+    new Set([...a, ...b.filter(x => a.findIndex(y => comp(x, y)) === -1)])
+  );
+```
+
+```js
+unionWith([1, 1.2, 1.5, 3, 0], [1.9, 3, 0, 3.9], (a, b) => Math.round(a) === Math.round(b)); // [1, 1.2, 1.5, 3, 0, 3.9]
+```
diff --git a/tag_database b/tag_database
index 58c4f00fc..13ccb8adb 100644
--- a/tag_database
+++ b/tag_database
@@ -219,6 +219,8 @@ truncateString:string
 truthCheckCollection:object,logic,array
 unescapeHTML:string,browser
 union:array,math
+unionBy:array,function
+unionWith:array,function
 uniqueElements:array
 untildify:node,string
 URLJoin:string,utility,regexp