淘汰赛：如果一个领域被填满，如何进行输入，如果一个领域是空的，则不需要输入

I want to make a password change form. It should be displayed on the settings page at any time and be not required to be filled. However if at least one of three fields (old pass, new pass, confirm) is filled others should become required. I want to make a password change form. It shoul