Add a watch mode

What problem does this feature solve?

Sometimes you don’t want to serve html and other build files with integrated serve command.

Requirements

watch command option needs to take into account vue.config.js’s outputDir or --dest. (I’m guessing this would work out of the box even). I think it’s actually same as running webpack-cli with webpack --watch.

Would you be willing to merge a PR that adds this command / command option?

What does the proposed API look like?

vue-cli-service watch

or (preferably)

vue-cli-service build --watch

[meteorlxy]

I met two problems with vue-cli-service build --watch --mode development.

1. Lots of [hash].hot-update.json are being generated:

1. The assets files are not in the sub directory:

dashboard.js is supposed to be put into public/js dir, but it’s in public/ now.

---

Here’s my vue.config.js:

module.exports = {
  outputDir: 'public',
  
  pages: {
    dashboard: {
      entry: 'client/src/dashboard/app.js',
      template: 'client/public/index.html',
      filename: '../resources/views/dashboard.blade.php',
      chunks: ['chunk-vendors', 'chunk-common', 'dashboard']
    }
  },

  chainWebpack (config) {
    config.resolve
      .alias
        .set('@', path.resolve(__dirname, 'client/src'))
        .end()
  },
}

With version 3.0.3

[yyx990803]

Sure, we can take a PR for build --watch