Builder implemented with webpack4 and webpack4-compatible loaders/plugins/config, used by @storybook/core-server to build the manager UI.
webpack4 is the default, so no configuration is necessary to use it. However, if you wan to explicitly configure your Storybook to run webpack4, install it as a dev dependency and then update your .storybook/main.js configuration.
module.exports = {
core: {
builder: 'webpack4',
},
};