Rendering comma separated list of links

Simply

{tags.map((tag, i) => <span key={i}>
    {i > 0 && ", "}
    <Tag tag={tag} />
</span>)}

In React 16 it can be done even more simpler:

{tags.map((tag, i) => [
    i > 0 && ", ",
    <Tag key={i} tag={tag} />
])}