<form name="fmtarget" id="ff">
<input type="text" name="a[a]"/>
<input type="text" name="a[b]" value="13"/>
<input type="text" name="a[c]"/>
</form>
<script>
var json={
"a" : 12,
"b": "Jack",
"c": "Description"
};
var fmtarget=document.forms['fmtarget'];
for(key in json)
{
if(json.hasOwnProperty(key))
fmtarget["a["+key+"]"].value=json[key]
}
</script>
