Add support for function to

[taion]

Closes #3657

I'm not absolutely sure this is entirely correct – the "nice" way to use this requires creating a throwaway function in render. But <Link> isn't a pure component right now anyway.

[taion]

Rebased.

[timdorr]

I would make this a class method so you don't have to pass it any args Bonus points: You can make it a getter (router.push(this.to)).

Also, and this is personal preference, but I'm generally not a fan of extracting methods from a class unless they are also being exported from the module.

[taion]

This isn't a class method because we need to strip out to from props in render anyway – we can't (shouldn't) pass it down because otherwise we get React 15.2.x "unknown props" warnings.

The other options would be to either destructure it out and leave it unused, or do an explicit delete, both of which are uglier than just using it as a function arg.

[timdorr]

Nevermind, we're still using createClass, so that's not even possible. I meant something like this:

get to() {
  const { to } = this.props
  return typeof to === 'function' ? to(this.context.router.location) : to
}

handleClick(event) {
  //...
  router.push(this.to)
}

[taion]

I think this just ends up being the cleanest way to strip off the to prop before it gets to the underlying <a>.