Refactor to improve perf w/ pre-declared positions

Closes GH-9.

Reviewed-by: Titus Wormer <tituswormer@gmail.com>

Author: ChristianMurphy

lib/index.js

@@ -65,13 +65,17 @@ export function gfmTableFromMarkdown() {
 function enterTable(token) {
   const align = token._align
   assert(align, 'expected `_align` on table')
+  // Trailing `position: undefined` keeps the table hidden class stable;
+  // mdast-util-from-markdown's enter() patches the field to a real value
+  // but the property already exists, so no shape transition fires.
   this.enter(
     {
       type: 'table',
       align: align.map(function (d) {
         return d === 'none' ? null : d
       }),
-      children: []
+      children: [],
+      position: undefined
     },
     token
   )
@@ -92,7 +96,8 @@ function exitTable(token) {
  * @type {FromMarkdownHandle}
  */
 function enterRow(token) {
-  this.enter({type: 'tableRow', children: []}, token)
+  // See enterTable above for the rationale on the trailing position field.
+  this.enter({type: 'tableRow', children: [], position: undefined}, token)
 }
 
 /**
@@ -108,7 +113,8 @@ function exit(token) {
  * @type {FromMarkdownHandle}
  */
 function enterCell(token) {
-  this.enter({type: 'tableCell', children: []}, token)
+  // See enterTable above for the rationale on the trailing position field.
+  this.enter({type: 'tableCell', children: [], position: undefined}, token)
 }
 
 // Overwrite the default code text data handler to unescape escaped pipes when
@@ -230,11 +236,8 @@ export function gfmTableToMarkdown(options) {
   function serializeData(matrix, align) {
     return markdownTable(matrix, {
       align,
-      // @ts-expect-error: `markdown-table` types should support `null`.
       alignDelimiters,
-      // @ts-expect-error: `markdown-table` types should support `null`.
       padding,
-      // @ts-expect-error: `markdown-table` types should support `null`.
       stringLength
     })
   }