Maybe try resolve or path.resolve?

extendWebpack (cfg) { cfg.resolve.alias = { ...cfg.resolve.alias, // Add your own alias like this 'vue$': 'vue/dist/vue.esm.js', '@': resolve('src') }

or…

extendWebpack (cfg) { cfg.resolve.alias = { ...cfg.resolve.alias, // Add your own alias like this 'vue$': 'vue/dist/vue.esm.js', '@': path.resolve('src') }