Fluid Viewhelper f:format.json returns htmlentities and more problems with curly braces in fluid - typo3

Question

in TYPO3 8 LTS i try build a json output from news list. When using the viewhelper f:format.json in exact the same way as in the fluid manual:
{f:format.json(value: {foo: 'bar', bar: 'baz'})}
i get this:
{"foo":"bar","bar":"baz"}
this works:
{f:format.json(value: newsItem.datetime)->f:format.htmlentitiesDecode()}
but i need the date-object formatted in this way:
{newsItem.datetime->f:format.date(format: "%Y-%m-%d")}
and now i am looking for a possibility to match both in order to get this output:
{'date':'2018-03-16'}
I tried a many ways like this, but nothing works.
{f:format.json(value: {date:newsItem.datetime->f:format.date(format: "%Y-%m-%d")})->f:format.htmlentitiesDecode()}
any idea how to get it right?
Thanks
Peter

Answer 1

well Bernd showed me the way in his comment above - here is one of the solutions which i found with this little help of him:
{f:format.json(value: {date:'{newsItem.datetime->f:format.date(format: "%Y-%m-%d")}'})->f:format.htmlentitiesDecode()}
f:format.raw works much the same like f:format.htmlentitiesDecode; really important are the two '' around {newsItem.datetime->f:format.date(format: "%Y-%m-%d")}.
With the idea of format.raw i found an other solution too:
<f:format.raw value='{"date":"' />{newsItem.datetime->f:format.date(format: "%Y-%m-%d")}<f:format.raw value='"},' />
Looks quite a bit complicated but with
<f:format.raw value='{' />
<f:format.raw value='}' />
it is possible to use curly brackets in fluid templates.
Thanks!