trying to find if the key views exists, only do some work, what is wrong i am doing

for (d in posts) {
            for (key in d) {
               
               structkeyexists(key,'views');
               dump(key);
            }
        }

Without the output you're actually getting, it's hard to tell anything. Is posts empty? Is d empty? Both of those would result in no output. Or are you getting an error? Is posts not a struct, an array, or a list? Same question for d. Is key not a struct?

@Simone we've been through this before. Don't ask "what am I doing wrong?", tell us what the code is doing, what your expectations are (you did that bit... kinda), and how the code's behaviour is differing from your expectations. And a summary of what troubleshooting you have already done.

if(structkeyexists(d,'views')) { this will work

I'm taking that to mean that

d

is a struct and

d

has a

views

key. I'm just going to guess at your data structure here, because you still haven't told us... And that posts is an array of structs, like so:

var posts = [
    {
        subject: "Post 1",
        content: "This is the first post",
        views: 14
    },
    {
        subject: "Post 2",
        content: "Post 1 is stupid. I disagree.",
        views: 6
    }
];

Then, your code would be

for (d in posts) {
    for (key in d) {
        structkeyexists(key, "views");
        dump(key);
    }
}

And processing it would look like this:

1. posts has 2 items, so it enters the loop.
2. d = the first struct (post 1)
3. d has keys, so it enters the second loop.
4. key = "subject"
5. structkeyexists("subject", "views") throws an error because "subject" is not a struct. It's a string.