Duplicate keys raise an error

[wjandrea]

Example:

{"name": "Alice", "age": 30, "age": 30}

JSONLint says:

Invalid JSON!
Error: Duplicate key 'age'

However, duplicate keys are valid. ECMA-404 says:

The JSON syntax does not impose any restrictions on the strings used as names, does not require that name strings be unique, ...

So this data is valid.

That said, I agree that duplicate keys aren't good. They should raise a warning instead.