Make html.Selection.map return []goja.Value instead of []string

[oleiade]

This PR attempts to address #2471.

The existing Html.Selection.map function would return a []string under the hood. This behavior would result in effectively obfuscating any type that's not a string during the parsing of an HTML or XML document. This PR modifies the behavior and signature of the function to fit what we have documented. The return value should be an Array of values on the JS script side, a []goja.Value in the Go implementation of the library.

The reason why we returned []string in the first place is because goquery, the library we depend on to perform HTML/XML parsing, own map method does so. To work around the limitation, I adopted an approach consisting in serializing the values with map over to JSON, and deserialize them before we return from the Map function.

It works, but I'm open to any other approach that might be simpler or more performant 🙇🏻

[olegbespalov]

👍

[oleiade]

Here's an example script demonstrating it at play

import { parseHTML } from 'k6/html'

const data = `
<ListAllMyBucketsResult>
   <Buckets>
      <Bucket>
         <CreationDate>myCreationDateTimestamp</CreationDate>
         <Name>myBucketName</Name>
      </Bucket>
   </Buckets>
   <Owner>
      <DisplayName>string</DisplayName>
      <ID>string</ID>
   </Owner>
</ListAllMyBucketsResult>`

export default function () {
    const buckets = parseHTML(data)
        .find('Buckets')
        .children()
        .map(function (_, bucket) {
            let bucketObj = {}
            bucket.children().each(function (_, elem) {
                switch (elem.nodeName()) {
                    case 'name':
                        Object.assign(bucketObj, { name: elem.textContent() })
                        break
                    case 'creationdate':
                        Object.assign(bucketObj, { creationDate: elem.textContent() })
                        break
                }
            })

            return bucketObj
        })

    console.log(JSON.stringify(buckets)) // Prints [{"creationDate":"timestamp","name":"string"}]
    console.log(buckets[0].name) // Prints "myBucketName"
    console.log(buckets[0].creationDate) // Prints "myCreationDateTimestamp"
}

cc @mstoykov