I know a guy who works on core web-dev stuff at Google.
He tells me that Edge is oftenvery quirky in very subtle ways. He's had to spend many, many hours diagnosing, reporting, and working around quirks in Edge. These quirks sometimes get fixed and sometimes do not, but are often not present in Internet Explorer.
We have a fairly large-ish JS codebase at work and from what I saw so far is that Edge's JS was never a problem. SVG rendering on the other hand is horribly broken currently for some cases.
That being said, since our JS is generated, it's purely ES5 since it still has to run on IE9. So maybe the weird cases are in the more modern JS parts we don't use.
He tells me that Edge is often very quirky in very subtle ways. He's had to spend many, many hours diagnosing, reporting, and working around quirks in Edge. These quirks sometimes get fixed and sometimes do not, but are often not present in Internet Explorer.