I made this JS code in an HTML file:

```
<script>
x=[];
x["abc"]={
    a:1,
    b:2
}
x["def"]={
    a:234,
    b:5655
}

keyArrayX=x.keys();
console.log(keyArrayX.join());
</script>

```

When I render the file, I get this error:

```
Uncaught TypeError: keyArrayX.join is not a function

```

But the result of `keys()` is an array, so I don't understand what's wrong here. My goal is to return a concatenated string of all the keys in the array, in this case it would be:

```
abc,def

```