I had this error running a Webpack config. Seemed like something went wrong with the 

npm install

and it was unable to install webpack.

Solution

To fix this, run:

  1. Uninstall Webpack and the CLI:

    npm uninstall -g webpack npm uninstall webpack-cli

  2. Re-Install webpack and the cli locally since installing webpack globally may cause issues:

    "Note that this is not a recommended practice. Installing globally locks you down to a specific version of webpack and could fail in projects that use a different version."

    npm install --save-dev webpack npm install --save-dev webpack-cli

Source: https://stackoverflow.com/questions/54599370/missing-script-webpack-in-npm