When do I get this error?

The "Unexpected comment" error is thrown when JSLint encounters a single-line or multi-line comment in a JSON string. It will only generate this error when in JSON mode (it enters JSON mode when the first character of the input is either { or [). In the following example we attempt to comment one of our JSON properties:

{
    "name": "James", // My first name
    "age": 24
}

Why do I get this error?

This error is raised to highlight a fatal syntax error. The JSON specification does not provide any mechanism for comments. Attempting to deserialize the above example (using JSON.parse for example) will throw a syntax error. To solve this issue, simply remove any comments from your JSON:

{
    "name": "James",
    "age": 24
}