[whizzter]

Most reasonable parsers has an allow-comments flag, and even in JS you could it in a simple regexp replace all with:

const obj = JSON.parse(jsonText.replaceAll(/("(?:\\"|\\.|[^"])"|[^\/])|\/\/.|(\/)/g,"$1$2"));

The above should be multiline JSON safe and give you single-line comments to end-of-line, it matches first strings (and checks for escaped double-quotes and escapes to get them correctly) or all other characters except // sequences (outside of strings) and passes that straight through via group 1(anything outside of string not starting with /) or 2(single / even if it's outside of JSON spec), if a // sequence is found it's not passed through and disappears.

Yes, regexps can be abused. This one should be fine though but only use it for config files you control :), use as CC0 and keep an keen eye if translating to another language since escapes will differ if the regexp goes into a string instead of a regexp literal like in JS.