Small selector problems in jQuery (new users will inevitably encounter) _ jquery

The jQuery selector problem encountered during user registration verification is recorded below. If you have encountered a similar situation, refer to the jQuery manual to learn about the usage of the selector, i'm going to try to write a user registration verification. I didn't expect a very small problem to be solved yet!

It is inevitable that new users will encounter very small details. In this article, we will only encourage them:

The test code is as follows:

The Code is as follows: