The map operator creates a new array populated from the target array data.
Here in this blog, I use JavaScript to render a top level labels in the search page. For that, the script will have look into each post's labels. One easy way to provide the labels data is by using the map operator of the lambda expression.
In this case, the result is an array of string that can be parsed using JSON.parse().
Template code:
<div hidden="" class="_labelsMap">
<b:eval expr='data:post.labels map (l => l.name)'/>
</div>Result:
<div hidden="" class="_labelsMap">
["weekly-blog-design"]
</div>In JavaScript:
let labelsName = JSON.parse(document.querySelector('._labelsMap').textContent);
// do something with labels name