Provide option to disable initial compilation when watching

[JasonTheAdams]

Do you want to request a feature or report a bug?
Feature Request

What is the current behavior?
When webpack --watch is first run, the first thing it does it compile all of the entries.

If the current behavior is a bug, please provide the steps to reproduce.

What is the expected behavior?
For webpack to simply start watching the files and not immediately compile. But given that this doesn't apply as much to single-entry instances, at least have an option for it.

If this is a feature request, what is motivation or use case for changing the behavior?
Given the number of entries (and if sourcemaps are enabled) this can can take a significant amount of time. With this feature one would be able to enable watching and immediately get to work without having to worry about whether it's finishing compiling and is actually watching, yet.

Please mention other relevant information such as the browser version, Node.js version, webpack version and Operating System.
Node: 4.5.0
Webpack: 2.6.1
OS: Windows 10

[TheLarkInn]

Are you seeing bottlenecks at this point of the compilation process?

[JasonTheAdams]

Hi @TheLarkInn, only in the sense that it may take upwards of 30-60 seconds (and scaling with each entry) every time I go to start watching. Often times I'll turn it on, flip back to the code, make a couple tweaks, save, switch to the browser, refresh, and then realize that it just finished the first compilation so the changes I just made weren't included. So then I go save again, and I'm good to go. It's just was feels like an unnecessary hickup in the workflow.

[sokra]

Sounds like a bug. I should actually work this way. It compares timestamp to build start timestamp when starting watching, so this should detect changes between start of compilation and start of watching.

[kirill-konshin]

This is very much needed. Babel CLI has --skip-initial-build option for example.

My use case is a Lerna monorepo with libraries (Babelized and Webpacked) and demos, I need to build all libs as phase 1 and then run demos + watch on phase 2, so the more libs you have the more inefficient it becomes. Currently the watch procedure looks like this:

{
  "scripts": {
    "build": "lerna run build --scope=@xxx/lib-* --concurrency=1 --stream",
    "start": "npm run build && lerna run start --parallel"
  }
}

Since Lerna's --parallel completely disregards topology this phased approach is a must, demos are independent of each other while libs have dependencies on each other and demos depend on libs.

[blixt]

I have a use case where I want, inside a Makefile, to build once, then run a bash script, then start watching. Right now the watch will kick off an unnecessary build.

[alshdavid]

I have created this PR which adds:
#9735

module.exports = {
  // ...
  watchOptions: {
    skipInitialEmit: false
  }
}

[alexander-akait]

@alshdavid duplicate #9730 ?

[alshdavid]

@evilebottnawi, any chance you've had a chance to review the PR?

[kirill-konshin]

#9730 is a duplicate dated Sep 24. This one here seems to be the original issue from 2017.

[meszaros-lajos-gyorgy]

So it's been over 3 years now since the first report. Any update on this?