fix(markdown): preserve user-defined attributes

closes #5123

src/node/markdown/plugins/image.ts

@@ -40,7 +40,7 @@ export const imagePlugin = (
       addImageDimensions(token, url, publicDir, env)
     }
 
-    if (lazyLoad && !token.attrGet('loading')) {
+    if (lazyLoad && token.attrIndex('loading') < 0) {
       token.attrSet('loading', 'lazy')
     }
 

src/node/markdown/plugins/link.ts

@@ -51,7 +51,7 @@ export const linkPlugin = (
       hrefAttr[1] = url
       if (isExternal(url)) {
         Object.entries(externalAttrs).forEach(([key, val]) => {
-          token.attrSet(key, val)
+          if (token.attrIndex(key) < 0) token.attrSet(key, val)
         })
         // catch localhost links as dead link
         if (url.replace(EXTERNAL_URL_RE, '').startsWith('//localhost:')) {

src/node/markdown/plugins/table.ts

@@ -6,7 +6,7 @@ export const tablePlugin = (md: MarkdownItAsync) => {
   const tableOpen = md.renderer.rules.table_open
   md.renderer.rules.table_open = function (tokens, idx, options, env, self) {
     const token = tokens[idx]
-    if (token.attrIndex('tabindex') < 0) token.attrPush(['tabindex', '0'])
+    if (token.attrIndex('tabindex') < 0) token.attrSet('tabindex', '0')
     return tableOpen
       ? tableOpen(tokens, idx, options, env, self)
       : self.renderToken(tokens, idx, options)