Are trailing commas in arrays and objects part of the spec?

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Are trailing commas standard in JavaScript, or do most browsers like Chrome and Firefox just tolerate them?

I thought they were standard, but IE8 puked after encountering one—of course IE not supporting something hardly means it’s not standard.

Here’s an example of what I mean (after the last element of the books array):

var viewModel = {
    books: ko.observableArray([
        { title: "..", display: function() { return ".."; } },
        { title: "..", display: function() { return ".."; } },
        { title: "..", display: function() { return ".."; } }, // <--right there
    ]),
    currentTemplate: ko.observable("bookTemplate1"),
    displayTemplate: function() { return viewModel.currentTemplate(); }
};

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