Using the DatePicker date control, Prop being mutated: "placement" error occurs

I. Reason for error

• element-ui version: 2.15.9
• The screenshot of the error report is as follows:
  

II. Reason analysis

• After element-ui is upgraded to version 2.15.6 or above, a line of code to directly modify placement is added to the date-picker component (you can go and see)
• View the screenshot of the address as follows:
  

Third, the solution

1. Go to the package.json file in the project to check the element-ui version, if it is higher than 2.15.6, uninstall the current version directly
2. Enter npm install [email protected] -S to install the 2.15.6 version, then remove the ^ sign in front of the version (if you don't understand the symbol in front of the version, you can look at Baidu)
3. Remove node_modules package
4. Enter npm install to install dependencies

4. Screenshot of element-ui version