New option to run another script when start watching

[binarykitchen]

Such a hook would be great and useful for this scenario: call browser-sync ... once rollup has bundled and starts watching for changes.

Don't want browser-sync to open the browser before bundling is complete you know.

[meszaros-lajos-gyorgy]

+1 for this feature, because at the moment we cannot distinguish, if rollup was started with a watch option.

[meszaros-lajos-gyorgy]

Might be a duplicate for #48

[binarykitchen]

Not really a duplicate, more like a post-hook, to run something else when watching has started.

[ScottMaclure]

Use case: I want to re-run sw-precache every time rollup has finished building assets.

Edit: Add a "pre-hook" as well, so I can run a linter beforehand (fail early).

[CoskunSunali]

Would be really useful.