How can I use a unary operator?

[Melodyn]

I did not find examples of its use in the readme. Is it possible to build "not in" conditions?

const context = {
  peoples: [
    { first: 'Lana', last: 'Kane', hobby: ['guitar', 'flowers'] },
    { first: 'Cyril', last: 'Figgis', hobby: ['computer', 'cats'] },
    { first: 'Pam', last: 'Poovey', hobby: ['poetry', 'dogs'] }
  ]
}

jexl.eval('!(peoples["dogs" in .hobby])', context);
/* result:
{ first: 'Lana', last: 'Kane', hobby: ['guitar', 'flowers'] },
{ first: 'Cyril', last: 'Figgis', hobby: ['computer', 'cats'] },
*/

[TomFrost]

Hi Melodyn!

It looks like you’re negating a collection of objects with your !, rather than the filter criterion. Try this instead:

jexl.eval('peoples[!("dogs" in .hobby)]')

I apologize, normally I’d try this myself before posting, but I’m mobile for the next few hours. Happy to dig in further if that doesn’t work though!

[TomFrost]

Ok, I got a moment to test this and my solution above definitely does not work. It would appear that filtering an array by using an in condition (even without the unary operator) fails, and I'm guessing it has to do with how jexl detects the use of relative identifiers.

The good news is, there's a very easy workaround for this. Just add this to your code when you initialize Jexl:

jexl.addTransform('contains', (ary, search) => ary.includes(search))

And now you can filter with no problem:

jexl.evalSync('peoples[!.hobby|contains("dogs")]', context)

Output:

[
  { first: 'Lana', last: 'Kane', hobby: [ 'guitar', 'flowers' ] },
  { first: 'Cyril', last: 'Figgis', hobby: [ 'computer', 'cats' ] }
]

Let me know if that solves your immediate need, and I'll start looking into the in issue!

[Melodyn]

Hi Tom!

Yes, this solution suits me. Thank you for your prompt reply and your wonderful library :)