The element ’sn_form_inline_stream_entries’ contains the entire activity stream and you will be manipulating a potentially huge chunk of the DOM that might already contain working links. Instead you could grab the specific elements that can contain text URIs.
function onLoad() {
var regEx = /(\b(https?|ftp|file):\/\/[-A-Z0-9+&@#\/%?=~_|!:,.;]*[-A-Z0-9+&@#\/%=~_|])/ig;
var linkTemplate = '<a href="$1" target="_blank">$1</a>';
var activityStream = document.getElementById('sn_form_inline_stream_entries');
var textBlocks = activityStream.querySelectorAll('.sn-widget-textblock-body');
textBlocks.forEach(function (textBlock) {
textBlock.innerHTML = textBlock.innerHTML.replace(regEx, linkTemplate);
});
}I assume that your regular expression does what you need it to do.
For this to work in current versions of ServiceNow you will have to set “Isolate script” to false on the client script:
This is not best practice and will break if the structure of the activity stream changes. It is a rather expensive operation to have running on every form load.
If you are able to manipulate the text before it goes into the journal entry you can format working links with the [code] tag and avoid the script running client side:
This link [code]<a href="https://www.example.com/" target="blank">https://www.example.com/</a>[/code] is an example. 
