code: function watchBuild(config) {
    // verify config
    if (!lintConfig(config)) throw new Error('invalid config')
  
    // set development env
    CONTEXT.env = 'development'
  
    // build once immediately
    buildOnce(config)
  
    // bind watch handler
    assist.tryWatch(
      config.$path.source.client,
      function (e, file) {
        if (!file) return
        CONTEXT.entries.push(path.join(config.$path.source.client, file))
        buildOnce(config, CONTEXT)
        CONTEXT.entries = []
      }
    )
  }
docs: watch & build, development