JSON is often interpreted as dictionary but is serialized as key-value pairs, for JSON itself this is not a big problem as everybody agrees not to produce JSON

JSON is often interpreted as dictionary but is serialized as key-value pairs, for JSON itself this is not a big problem as everybody agrees not to produce JSON documents like {"a":1,"b":2,"a":3} so most people do not care about how their parser reads them. In cases like URL queries or HTTP headers it is not such a clear cut. There it is common both to use duplicated keys and to use JSON-like dictionaries to read them. Personally I never had bugs due to this: PHP does the "right" thing with duplicated keys and I never encountered it in node, but it bugs me that we use this kind of lossy[0] representations. [0] in JS in particular the object are not really adequate to be used as dictionaries, inheritance and predefined keys aside there are also special magical attributes that behave in special ways Object.getPrototypeOf(Object.assign({}, JSON.parse('{"__proto__":null}')))===null;