Why is the tree reduced instead of mapped in handleExtendsNodes?

[HoldYourWaffle]

Why does handleExtendsNodes use the Array.reduce function instead of Array.map? As far as I can see it's always a direct transformation, the purpose of Array.map.
Also, shouldn't the line m = m.concat(...) just be m.push(...)?

Using map and push instead of concat would simplify the code from this (I removed irrelevant lines):

function handleExtendsNodes (tree, options, ctx) {
  return tree.reduce((m, node) => {
    if (node.name !== 'extends') {
      if (Array.isArray(node.content)) {
        node.content = handleExtendsNodes(node.content, options, ctx)
        m.push(node)
      } else {
        m.push(node)
      }
      return m
    }

    // ... snip ...

    m = m.concat(mergeExtendsAndLayout(layoutTree, handleExtendsNodes(node.content, options, ctx), ctx))
    return m
  }, [])
}

to this:

function handleExtendsNodes (tree, options, ctx) {
  return tree.map(node => {
    if (node.name !== 'extends') {
      if (Array.isArray(node.content)) {
        node.content = handleExtendsNodes(node.content, options, ctx)
	  }
	  return node
    }

    // ... snip ...

    return mergeExtendsAndLayout(layoutTree, handleExtendsNodes(node.content, options, ctx), ctx)
  })
}

I haven't tested this code so I'm not 100% sure it works as intended, but I don't see any reason why there's the need for reduce. I might however be missing something (probably very obvious), hence the question.

[jescalan]

I think you're right here, probably I was tinkering with other logic initially when I made it a reduce, then never changed it back. Wanna PR and change it, see if the tests pass?

[HoldYourWaffle]

I did some investigating, and it seems like I'm actually wrong. It's not a direct transformation because a single <block> element gets 'unwrapped' to multiple children.

I was right however about the possibility to simplify the last 2 lines:

// Current
m = m.concat(mergeExtendsAndLayout(*snip*))
return m

// Option 1
m.push(...mergeExtendsAndLayout(*snip*))
return m

// Option 2
return m.concat(mergeExtendsAndLayout(*snip*))

I think I like option 2 better, and it's probably faster too. I don't think it's worth it to create a PR for this though, I'll most likely include it in #24.

[jescalan]

That sounds good to me 👍