Refactor code-style

*   Add more docs to JSDoc

lib/index.js

@@ -3,37 +3,38 @@
  */
 
 /**
- * @template {Node} [Tree=Node]
- * @typedef {import('./complex-types.js').MapFunction<Tree>} MapFunction
+ * @template {Node} [Kind=Node]
+ *   Node type.
+ * @typedef {import('./complex-types.js').MapFunction<Kind>} MapFunction
  *   Function called with a node, its index, and its parent to produce a new
  *   node.
  */
 
 /**
  * Create a new tree by mapping all nodes with the given function.
  *
- * @template {Node} Tree
+ * @template {Node} Kind
  *   Type of input tree.
- * @param {Tree} tree
+ * @param {Kind} tree
  *   Tree to map.
- * @param {MapFunction<Tree>} mapFunction
+ * @param {MapFunction<Kind>} mapFunction
  *   Function called with a node, its index, and its parent to produce a new
  *   node.
- * @returns {Tree}
+ * @returns {Kind}
  *   New mapped tree.
  */
 export function map(tree, mapFunction) {
   // @ts-expect-error Looks like a children.
   return preorder(tree, null, null)
 
-  /** @type {import('./complex-types.js').MapFunction<Tree>} */
+  /** @type {import('./complex-types.js').MapFunction<Kind>} */
   function preorder(node, index, parent) {
-    var newNode = Object.assign({}, mapFunction(node, index, parent))
+    const newNode = Object.assign({}, mapFunction(node, index, parent))
 
     if ('children' in node) {
       // @ts-expect-error Looks like a parent.
       newNode.children = node.children.map(function (
-        /** @type {import('./complex-types.js').InclusiveDescendant<Tree>} */ child,
+        /** @type {import('./complex-types.js').InclusiveDescendant<Kind>} */ child,
         /** @type {number} */ index
       ) {
         return preorder(child, index, node)

package.json

@@ -67,11 +67,7 @@
     "trailingComma": "none"
   },
   "xo": {
-    "prettier": true,
-    "rules": {
-      "no-var": "off",
-      "prefer-arrow-callback": "off"
-    }
+    "prettier": true
   },
   "remarkConfig": {
     "plugins": [