Good eye++. It is the same issue as Perl hashes though. Duplicate Object keys in JS are a mistake and will be clobbered.

<script type="text/javascript">
    var p = { "age1":"one", "age1":"two" };
    for ( var key in p ) {
        if ( p.hasOwnProperty(key) ) {
            document.write(key + " -> " + p[key] + "<br/>");
        }
    }
</script>
age1 -> two
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