Refactor code-style

*   Add more docs to JSDoc

Author: wooorm

lib/index.js

@@ -1,5 +1,10 @@
 /**
- * @typedef {import('mdast').Content|import('mdast').Root} Node
+ * @typedef {import('mdast').Root} Root
+ * @typedef {import('mdast').Content} Content
+ */
+
+/**
+ * @typedef {Content | Root} Node
  */
 
 import {visit} from 'unist-util-visit'
@@ -8,21 +13,15 @@ import {visit} from 'unist-util-visit'
  * Make an mdast tree compact by merging adjacent text nodes and block quotes.
  *
  * @template {Node} Tree
+ *   Node type.
  * @param {Tree} tree
+ *   Tree to change.
  * @returns {Tree}
+ *   Changed tree.
  */
+// To do: next major: don‘t return `tree`.
 export function compact(tree) {
-  // @ts-expect-error: hush, TS.
-  visit(tree, visitor)
-
-  return tree
-
-  /**
-   * @param {import('mdast').Content} child
-   * @param {number} index
-   * @param {Extract<Node, import('mdast').Parent>} parent
-   */
-  function visitor(child, index, parent) {
+  visit(tree, function (child, index, parent) {
     if (
       parent &&
       index &&
@@ -50,5 +49,7 @@ export function compact(tree) {
         return index
       }
     }
-  }
+  })
+
+  return tree
 }