Refactor code-style

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

Author: wooorm

Diff for: lib/index.js

@@ -3,28 +3,40 @@
  *
  * @typedef Options
  *   Configuration (optional).
- * @property {boolean} [includeImageAlt=true]
+ * @property {boolean | null | undefined} [includeImageAlt=true]
  *   Whether to use `alt` for `image`s.
  */
 
 /**
  * Get the text content of a node or list of nodes.
+ *
  * Prefers the node’s plain-text fields, otherwise serializes its children,
  * and if the given value is an array, serialize the nodes in it.
  *
  * @param {unknown} value
- * @param {Options} [options]
+ *   Thing to serialize, typically `Node`.
+ * @param {Options | null | undefined} [options]
+ *   Configuration (optional).
  * @returns {string}
+ *   Serialized `value`.
  */
-export function toString(value, options = {}) {
-  const {includeImageAlt = true} = options
-  return one(value, includeImageAlt)
+export function toString(value, options) {
+  const includeImageAlt = (options || {}).includeImageAlt
+  return one(
+    value,
+    typeof includeImageAlt === 'boolean' ? includeImageAlt : true
+  )
 }
 
 /**
+ * One node or several nodes.
+ *
  * @param {unknown} value
+ *   Thing to serialize.
  * @param {boolean} includeImageAlt
+ *   Include image `alt`s.
  * @returns {string}
+ *   Serialized node.
  */
 function one(value, includeImageAlt) {
   return (
@@ -38,9 +50,14 @@ function one(value, includeImageAlt) {
 }
 
 /**
+ * Serialize a list of nodes.
+ *
  * @param {Array<unknown>} values
+ *   Thing to serialize.
  * @param {boolean} includeImageAlt
+ *   Include image `alt`s.
  * @returns {string}
+ *   Serialized nodes.
  */
 function all(values, includeImageAlt) {
   /** @type {Array<string>} */
@@ -55,8 +72,12 @@ function all(values, includeImageAlt) {
 }
 
 /**
+ * Check if `value` looks like a node.
+ *
  * @param {unknown} value
+ *   Thing.
  * @returns {value is Node}
+ *   Whether `value` is a node.
  */
 function node(value) {
   return Boolean(value && typeof value === 'object')