Refactor to use structuredClone polyfill

Author: wooorm

lib/footer.js

@@ -5,6 +5,7 @@
  * @typedef {import('./state.js').State} State
  */
 
+import structuredClone from '@ungap/structured-clone'
 import {normalizeUri} from 'micromark-util-sanitize-uri'
 
 /**
@@ -110,8 +111,7 @@ export function footer(state) {
         type: 'element',
         tagName: state.footnoteLabelTagName,
         properties: {
-          // To do: use structured clone.
-          ...JSON.parse(JSON.stringify(state.footnoteLabelProperties)),
+          ...structuredClone(state.footnoteLabelProperties),
           id: 'footnote-label'
         },
         children: [{type: 'text', value: state.footnoteLabel}]

package.json

@@ -36,6 +36,7 @@
   "dependencies": {
     "@types/hast": "^3.0.0",
     "@types/mdast": "^4.0.0",
+    "@ungap/structured-clone": "^1.0.0",
     "devlop": "^1.0.0",
     "mdast-util-definitions": "^6.0.0",
     "micromark-util-sanitize-uri": "^2.0.0",
@@ -45,6 +46,7 @@
   },
   "devDependencies": {
     "@types/node": "^20.0.0",
+    "@types/ungap__structured-clone": "^0.3.0",
     "c8": "^8.0.0",
     "hast-util-to-html": "^8.0.4",
     "hastscript": "^7.0.0",