If you were using vite-plugin-vue2 , switch to @vitejs/plugin-vue2 (official):
Now, the Composition API is built natively into Vue 2.7. You can write modern, logic-composable code immediately, without changing your build system or risking plugin incompatibilities. upgrade vue 2.6 to 2.7
npm install vue-loader@^15.10.0 --save-dev If you were using vite-plugin-vue2 , switch to