Based on the javascript tag and the lack of comments to the contrary, I assume this question is about web browsers.
document.domConfig (and the associated DOMConfiguration interface) was introduced in the W3C DOM Level 3 Core in 2004.
The standard was not created only taking into account web browsers, in fact, none of the implementations necessary to become a W3C Recommendation were part of a web browser.
So, when the web browser renaissance began, a version of the DOM specification was created specifically for web browsers, now known as the DOM Living Standard , since there was no DOMConfiguration implementation (indicates a lack of interest from developers and, presumably, web developers, especially because that many functions are not related to the HTML DOM), the function was simply shortened from the specification .
It was not replaced by anything in particular; there is nothing to replace.
If you asked, “I can do X with domConfig, how to do it in a web browser,” you can get a better answer, but for a general question about an interface with a dozen rather obscure options, I think this is what the answer is it should be.