Rename js snippets

snippets/js/s/flatten-array.md

@@ -0,0 +1,29 @@
+---
+title: Flatten array
+type: snippet
+language: javascript
+tags: [array,recursion]
+cover: angry-waves
+dateModified: 2020-10-22T20:23:47+03:00
+---
+
+Flattens an array up to the specified depth.
+
+- Use recursion, decrementing `depth` by `1` for each level of depth.
+- Use `Array.prototype.reduce()` and `Array.prototype.concat()` to merge elements or arrays.
+- Base case, for `depth` equal to `1` stops recursion.
+- Omit the second argument, `depth`, to flatten only to a depth of `1` (single flatten).
+
+```js
+const flatten = (arr, depth = 1) =>
+  arr.reduce(
+    (a, v) =>
+      a.concat(depth > 1 && Array.isArray(v) ? flatten(v, depth - 1) : v),
+    []
+  );
+```
+
+```js
+flatten([1, [2], 3, 4]); // [1, 2, 3, 4]
+flatten([1, [2, [3, [4, 5], 6], 7], 8], 2); // [1, 2, 3, [4, 5], 6, 7, 8]
+```