Fix to clone result

lib/index.js

@@ -1,7 +1,3 @@
-// To do next major: use `structuredClone` (or so?) to deep clone `properties`
-// and the like: the return value has to be a clone (not shallow copy) of the
-// passed tree.
-
 /**
  * @typedef {import('hast').Nodes} Nodes
  * @typedef {import('hast').RootContent} RootContent
@@ -36,6 +32,7 @@
  *   Number of characters to truncate to (default: `140`).
  */
 
+import structuredClone from '@ungap/structured-clone'
 import {unicodePunctuation, unicodeWhitespace} from 'micromark-util-character'
 
 /** @type {ReadonlyArray<RootContent>} */
@@ -109,7 +106,7 @@ export function truncate(tree, options) {
     }
   }
 
-  return result
+  return structuredClone(result)
 
   /**
    * Transform in `preorder`.
@@ -141,8 +138,7 @@ export function truncate(tree, options) {
         const child = node.children[index]
 
         if (!ignore.includes(child)) {
-          const result = preorder(child)
-          // @ts-expect-error: assume content matches.
+          const result = /** @type {RootContent} */ (preorder(child))
           if (result) children.push(result)
         }
 
@@ -152,7 +148,7 @@ export function truncate(tree, options) {
         }
       }
 
-      // @ts-expect-error: assume content matches.
+      // @ts-expect-error: content model matches.
       replacement.children = children
     }
 

package.json

@@ -35,10 +35,12 @@
   ],
   "dependencies": {
     "@types/hast": "^3.0.0",
+    "@ungap/structured-clone": "^1.0.0",
     "micromark-util-character": "^2.0.0"
   },
   "devDependencies": {
     "@types/node": "^20.0.0",
+    "@types/ungap__structured-clone": "^0.3.0",
     "c8": "^8.0.0",
     "hast-util-select": "^6.0.0",
     "hastscript": "^8.0.0",