The danger of target=_blank and opener

> Also for SEO consideration, rel="nofollow" is also recommended.

If you are linking to another site, that helps said site's SEO ranking. If you use this in a way that the search engine views as cheating, the other site is penalized.

But as long as you and the other site are being fair, then you SHOULD link to them - they are obviously providing good content that you think is important, so why try to hog the credit and not give them the ranking they deserve.

Sitye like Stackoverflow do this to cut down on spam, (and perhaps because they want Google to view them as the original), but for a blog or whatever, why would you recommend this?

There were some high profile sites affected by this by the way, I think it was Instagram where it actually went wrong.

While the above link suggests noopener is beneficial to add as it will prevent the parent JS process from being paused by long running scripts in the child process, it may actually slow down the site being opened because of the additional time required to initialize the new child's process.

It also prevents sites that want to auto-close their opened tab/popup, like Facebook and other sharing sites, from being able to call `window.close` after sharing is complete.