Partial nuxt.config.js file showing the extend method you need to add

nuxt.config.js

  /*
   ** Build configuration
   */
  build: {
    /*
     ** You can extend webpack config here
     */
    extend(config, ctx) {
      if (ctx.isDev) {
        config.devtool = ctx.isClient ? 'source-map' : 'inline-source-map'
      }
    }
  }