I would like to add a purchase button in the content type, the button is an internal link, for example:www.example.com/go/nodeid. And then add an external purchase link to the text field, for example:https://item.jd.com/2385876.html. Click the buy button (internal link) JS jump to the external links, because I do not want to search engine crawling the external link address. For example, open the page（http://www.chong4.com.cn/read.php?18818）, showing the link（http://www.chong4.com.cn/cydb/go.php?18818_127334_22s）, click will jump to（https://detail.tmall.com/item.htm?id=536478627694&ali_trackid=2:mm_13376157_4604749_42838263,22s18818:1479362916_3k2_69258376）
nofollow: Links to an unendorsed document, like a paid link. ("nofollow" is used by Google, to specify that the Google search spider should not follow that link)
source: HTML rel Attribute
All you have to do is write your link like this:
<a rel="nofollow" href="http://www.example.com/something">Buy Now</a>
Implement the internal link jump to external link logic as per requirement. Now to avoid indexing of external links, you can install and configure Noindex External Links module.
Module let's you take full control of external links indexing. Pages could also pass HTML-validation.
Alternatively, you can use the Redirect module
Which allows you to redirec to external urls.
For add links in content type you can use link module. That provide you link field.Add link field in your content type.