Refactor to use Map

Author: wooorm

lib/index.js

@@ -14,8 +14,6 @@
 
 import {visit} from 'unist-util-visit'
 
-const own = {}.hasOwnProperty
-
 /**
  * Find definitions in `tree`.
  *
@@ -28,17 +26,17 @@ const own = {}.hasOwnProperty
  *   Getter.
  */
 export function definitions(tree) {
-  /** @type {Record<string, Definition>} */
-  const cache = Object.create(null)
+  /** @type {Map<string, Definition>} */
+  const cache = new Map()
 
   if (!tree || !tree.type) {
     throw new Error('mdast-util-definitions expected node')
   }
 
   visit(tree, 'definition', function (definition) {
     const id = clean(definition.identifier)
-    if (id && !own.call(cache, id)) {
-      cache[id] = definition
+    if (id && !cache.get(id)) {
+      cache.set(id, definition)
     }
   })
 
@@ -47,8 +45,7 @@ export function definitions(tree) {
   /** @type {GetDefinition} */
   function definition(identifier) {
     const id = clean(identifier)
-    // To do: next major: return `undefined` when not found.
-    return id && own.call(cache, id) ? cache[id] : undefined
+    return cache.get(id)
   }
 }