Trailing Comma Within JSON’s Array

I was debugging an AJAXy app which uses JSON as the data format, and it was fine with Firefox but not with Internet Explorer. After further debugging, the culprit turned out to be trailing commas within the data.

{"foo": {
    "bar": [
        {"id": "1", "url": ""},
        {"id": "2", "url": ""},
] }} returns 2 in Firefox, but it returns 3 in Internet Explorer. The solution was obviously to remove the last comma.

I’m guessing the problem is more to Javascript array.length which is handled differently between browsers.

Update: HTML comments embedded within what’s supposed to be JSON’s data will be ignored by Firefox, while they will cause failure during eval in Internet Explorer.

2 thoughts on “Trailing Comma Within JSON’s Array

  1. This is invalid JSON. (but it is valid JavaScript expression). If used as JS term then it is correct, but nobody knows which behaviour (IE or FF) is correct one. :(

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