Refactor code-style

*   Add more docs to JSDoc
*   Add support for `null` in input of API types

Author: wooorm

lib/index.js

@@ -1,14 +1,22 @@
 /**
  * @typedef {import('unist').Position} Position
  * @typedef {import('unist').Node} Node
- * @typedef {Record<string, unknown> & {type: string, position?: PositionLike|undefined}} NodeLike
  * @typedef {import('unist').Point} Point
- *
- * @typedef {Partial<Point>} PointLike
+ */
+
+/**
+ * @typedef NodeLike
+ * @property {string} type
+ * @property {PositionLike | null | undefined} [position]
  *
  * @typedef PositionLike
- * @property {PointLike} [start]
- * @property {PointLike} [end]
+ * @property {PointLike | null | undefined} [start]
+ * @property {PointLike | null | undefined} [end]
+ *
+ * @typedef PointLike
+ * @property {number | null | undefined} [line]
+ * @property {number | null | undefined} [column]
+ * @property {number | null | undefined} [offset]
  */
 
 export const pointStart = point('start')
@@ -17,8 +25,10 @@ export const pointEnd = point('end')
 /**
  * Get the positional info of `node`.
  *
- * @param {NodeLike|Node} [node]
+ * @param {NodeLike | Node | null | undefined} [node]
+ *   Node.
  * @returns {Position}
+ *   Position.
  */
 export function position(node) {
   return {start: pointStart(node), end: pointEnd(node)}
@@ -27,15 +37,18 @@ export function position(node) {
 /**
  * Get the positional info of `node`.
  *
- * @param {'start'|'end'} type
+ * @param {'start' | 'end'} type
+ *   Side.
+ * @returns
+ *   Getter.
  */
 function point(type) {
   return point
 
   /**
-   * Get the positional info of `node`.
+   * Get the point info of `node` at a bound side.
    *
-   * @param {NodeLike|Node} [node]
+   * @param {NodeLike | Node | null | undefined} [node]
    * @returns {Point}
    */
   function point(node) {