t.at is not a function being thrown in production only

[spencercorwin]

Marked version:
15.0.7

Describe the bug
I'm getting error reports from my client application in production with the error message "t.at is not a function. Please report this to https://github.com/markedjs/marked". This is bundled and minified production code so I'm having trouble pinning down exactly where in the marked source this coming from.

It appears to only happen when my blog is visited by web crawlers. I don't see any issues when I visit the blog myself in prod or locally.

To Reproduce
I can't reproduce it so far. I upgraded from 14.1.3 to 15.0.7 and started getting these errors in prod. You can visit the blog where each blog post is just markdown rendered on the client at https://microgreenmanager.com/blog.

Here is the code where I use marked:

import { type RendererObject, marked } from 'marked';
import * as React from 'react';
import { Root } from './Markdown';

interface Props {
  readonly source: string;
  readonly 'data-test'?: string;
}
export default function RenderMarkdown({ 'data-test': dataTest, source }: Props) {
  const renderer: RendererObject = {
    link({ href, text, title }): string {
      // If the link is for YouTube, then return a YouTube embed
      if (href.startsWith('https://www.youtube.com/watch?v=')) {
        const videoId = href.split('=')[1];
        const iframeStyles = 'position:absolute;top:0;left:0;width:100%;height:100%;';
        const wrapperStyles = 'position:relative;overflow:hidden;width:100%;padding-top:56.25%;';
        return `
          <div id="youtube-embed" style="${wrapperStyles}">
            <iframe
              style="${iframeStyles}"
              src="https://www.youtube.com/embed/${videoId}"
              title="${text}"
              frameborder="0"
              allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture"
              allowfullscreen
            ></iframe>
          </div>
        `;
      }
      return `<a href="${href}" ${title ? `title="${title}"` : ''} target="_blank" rel="noopener noreferrer">${text}</a>`;
    },
  };
  marked.use({ renderer });
  // biome-ignore lint/security/noDangerouslySetInnerHtml: <explanation>
  return <Root data-test={dataTest} dangerouslySetInnerHTML={{ __html: marked.parse(source, { async: false }) }} />;
}

Expected behavior
No errors being thrown.

[spencercorwin]

Ok after some more research I'm realizing maybe it's not marked code but possibly my build process that has changed which is not longer polyfilling .at() and the web crawlers don't support Array.at(). But still worth reporting here I guess.

[UziTech]

Array.at() has been available in all browsers and node for a few years.

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/at

maybe reporting it to the web crawlers would be more helpful?

[spencercorwin]

So weird. It must be another dependency update, like core-js or babel which caused this change. It looks like the only two user agent affected are the bingbot user agent and an Opera user agent. Sorry for the hasty issue! Marked is awesome, thank you!