JSON5
JSON5 — JSON for Humans
...Formally, the JSON5 Data Interchange Format is a superset of JSON (so valid JSON files will always be valid JSON5 files) that expands its syntax to include some productions from ECMAScript 5.1 (ES5). It's also a subset of ES5, so valid JSON5 files will always be valid ES5. This JavaScript library is a reference implementation for JSON5 parsing and serialization and is directly used in many of the popular projects mentioned above.