SEO机器人是否始终遵循A标记的href属性中的url，即使使用Javascript拦截了点击/点击？

Question

Suppose I have a regular A tag with a proper URL in its href attribute (foo.com). Now, suppose I intercept the click (or tap) event of the A with a JavaScript function so, instead of performing the default action (navigate to foo.com) I can do something else first (fade out the content, for example), then navigate to a different URL (otherfoo.com).

1. Would this affect SEO? (meaning, will the bots get confused?)
2. Would the bot follow the url in the href attribute (foo.com) or would it follow through the JavaScript function (and navigate to otherfoo.com)?

By "bots" and "SEO" I am mostly referring to Google, but broader answers would be great as well.

Answer 1

tl:dr

No, typical crawler doesn't evaluate javascript (to that extent) as it, in the effect, serves no real purpose - only more confusion.

Disclaimer

Crawlers can probably scan javascript or CSS to obtain other info, which could affect sorting - but this is irrelevant in the scope of this questions.

Further more google crawler parses javascript but this seems to have effect on generated DOM tree, not callbacks which can be infinitely complex and would leave a gap for unknown state of the output - google wouldn't know if it has the links right or not.

In many javascript interpreters I have noticed a javascript until onload scheme used to get proper DOM tree. HTML to PDF creators (the better ones) can be an example. Google will be similar I guess.

Thoughts on that

Ultimately, this is up to the implementation. But while it's technically possible to evaluate the javascript on your site and index javascript redirects, it's highly error prone and would not serve a practical purpose.

If nothing else, you could bypass check that by passing fake javascript files to the crawler, which usually identifies itself by User-Agent header.

Definitely do not rely on this. I think you should make a hidden (to the user) link to any content you want to index but is linked by javascript. Use hiding by CSS class though, in case some search engine thought it's smart to ignore inline style display:block nodes.

<a href="javascript.php" class="only-seen-by-crawlers">Javascript linked page</a>

Or just generally don't use javascript on links as it makes no sense in sane scenarios.