Change to yield undefined

Author: wooorm

lib/index.js

@@ -2,14 +2,13 @@
  * @typedef {import('hast').Nodes} Nodes
  */
 
-// To do next major: return `undefined`.
 /**
  * Get the rank (`1` to `6`) of headings (`h1` to `h6`).
  *
  * @param {Nodes} node
  *   Node to check.
- * @returns {number | null}
- *   Rank of the heading or `null` if not a heading.
+ * @returns {number | undefined}
+ *   Rank of the heading or `undefined` if not a heading.
  */
 export function headingRank(node) {
   const name =
@@ -18,5 +17,7 @@ export function headingRank(node) {
     name.length === 2 && name.charCodeAt(0) === 104 /* `h` */
       ? name.charCodeAt(1)
       : 0
-  return code > 48 /* `0` */ && code < 55 /* `7` */ ? code - 48 /* `0` */ : null
+  return code > 48 /* `0` */ && code < 55 /* `7` */
+    ? code - 48 /* `0` */
+    : undefined
 }

readme.md

@@ -67,7 +67,7 @@ In browsers with [`esm.sh`][esmsh]:
 import {h} from 'hastscript'
 import {headingRank} from 'hast-util-heading-rank'
 
-headingRank(h('p', 'Alpha')) //=> null
+headingRank(h('p', 'Alpha')) //=> undefined
 headingRank(h('h5', 'Alpha')) //=> 5
 ```
 
@@ -87,7 +87,7 @@ Get the rank (`1` to `6`) of headings (`h1` to `h6`).
 
 ###### Returns
 
-Rank of the heading or `null` if not a heading (`number?`).
+Rank of the heading or `undefined` if not a heading (`number | undefined`).
 
 ## Types
 

test.js

@@ -10,17 +10,17 @@ test('headingRank', async function (t) {
     ])
   })
 
-  await t.test('should return null for non-nodes', async function () {
+  await t.test('should return `undefined` for non-nodes', async function () {
     // @ts-expect-error runtime.
-    assert.equal(headingRank(), null)
+    assert.equal(headingRank(), undefined)
   })
 
-  await t.test('should return null for non-elements', async function () {
-    assert.equal(headingRank({type: 'text', value: '!'}), null)
+  await t.test('should return `undefined` for non-elements', async function () {
+    assert.equal(headingRank({type: 'text', value: '!'}), undefined)
   })
 
-  await t.test('should return null for non-headings', async function () {
-    assert.equal(headingRank(h('p', '!')), null)
+  await t.test('should return `undefined` for non-headings', async function () {
+    assert.equal(headingRank(h('p', '!')), undefined)
   })
 
   await t.test('should return the rank of a heading', async function () {