Fix exception on empty document

Author: wooorm

index.js

@@ -62,18 +62,24 @@ export function readingTime(tree, options = {}) {
     Math.max(firstGradeAge, Math.round(options.age || 16))
   )
   const text = toText(tree)
-  const scores = readabilityScores(text)
-  /** @type {number} */
-  const readabilityAge =
-    firstGradeAge +
-    median([
+  const scores = readabilityScores(text) || {}
+  const score = median(
+    [
       scores.daleChall,
       scores.ari,
       scores.colemanLiau,
       scores.fleschKincaid,
       scores.smog,
       scores.gunningFog
-    ])
+    ].filter((d) => d !== undefined)
+  )
+
+  if (score === null) {
+    return 0
+  }
+
+  /** @type {number} */
+  const readabilityAge = firstGradeAge + score
 
   // WPM the target audience normally reads.
   const targetWpm = baseWpm + (targetAge - firstGradeAge) * addedWpmPerGrade

readme.md

@@ -25,7 +25,7 @@ npm install hast-util-reading-time
 ## Use
 
 Say we have the following HTML from [“Word per minute: Alphanumeric entry” on
-Wikipedia](https://en.wikipedia.org/wiki/Words_per_minute#Alphanumeric_entry) in
+Wikipedia](https://en.wikipedia.org/wiki/Words\_per\_minute#Alphanumeric\_entry) in
 `example.html`:
 
 ```html

test.js

@@ -41,6 +41,12 @@ test('hastUtilReadingTime', (t) => {
     'should estimate (somewhat simple)'
   )
 
+  t.deepEqual(
+    readingTime({type: 'root', children: []}),
+    0,
+    'should estimate (empty)'
+  )
+
   t.deepEqual(
     readingTime(tree, {age: 12}),
     2.437_14,