Opening blog post links in new window with JavaScript

[me2019]

Hi. At some point in time, the following custom module was created and applied to our current blog template to open all links within a post in a new tab:

window.onload = function() {
    const postbodylinks = document.getElementById('section-post-body').getElementsByTagName('a');
    for (var index = 0; index < postbodylinks.length; index++) {
            postbodylinks[index].setAttribute('target', '_blank');
    };
};

My question: Is there something I can add to this bit of code that will make an exception for anchors? In our case, we're trying to implement a table of contents on some blog posts, but this module forces the anchors to open in a new tab, which we do not want.

Unfortunately, because my familiarity ends with CSS and HTML, I have no idea how this script works, as it doesn't look like other options for opening links in a new tab I can find online. The person who requested this module did so about a year ago, so the details of how it came into being have fallen into the murk.

If this is an acceptable question I would love an answer! I can share a link to a blog post with a table of contents if needed but I figured the issue/solution would be obvious to someone who knows Javascript. Thank-you in advance for any info you can offer.

[Tirabuchi]

Hello,
with that JQuery script you are targeting ALL links in the document and setting their attribute "target" to "_blank", I would suggest a different approach;
taking into account that you are working on a custom module, you could define a custom CSS class to be added just to links that you're intrested in, and then changing just their "target" attribute value.
ie. 

document.getElementsByClassName(className);

 For reference (I suppose you would have to target "a"

child elements inside the container): https://learn.jquery.com/using-jquery-core/selecting-elements/

Hope that helps