Add flatIterator

snippets/flatIterator.md

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+---
+title: Flat iterator
+tags: array,iterator,generator
+expertise: advanced
+firstSeen: 2022-03-09T05:00:00-04:00
+---
+
+Creates a generator that iterates over an iterable, flattening nested iterables.
+
+- Use recursion.
+- Use a `for...of` loop to iterate over the values of the given iterable.
+- Use `Symbol.iterator` to check if each value is an iterable. If it is, use the `yield*` expression to recursively delegate to the same generator function. Otherwise, `yield` the current value.
+
+```js
+const flatIterator = function* (itr) {
+  for (let item of itr) {
+    if (item[Symbol.iterator]) yield* flatIterator(item);
+    else yield item;
+  }
+};
+```
+
+```js
+const arr = [1, 2, [3, 4], [5, [6, [7], 8]], 9, new Set([10, 11])];
+[...flatIterator(arr)]; // 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11
+```