Error message:
[Vue warn]: Avoid mutating a prop directly since the value will be overwritten whenever the parent component re-renders. Instead, use a data or computed property based on the prop's value. Prop being mutated: "placement"
UI component version:
Since the project uses the elementUI2.15.7 version, an error will be reported when using the el-date-picker component. Although it does not affect the use, this error is still very annoying. Here is a recommended solution, which is useful for personal testing: Add to this component placement="bottom-start"
This perfectly solves the error reporting problem. Of course, you can also uninstall elementUI and re-download a version lower than 2.15.7. Of course, you can replace the library without affecting other components of the project.