Checkbox check and Judge code analysis _ javascript tips-js tutorial

When we are working on a project, especially when registering users, we basically need something like a registration agreement. How can we determine whether the user has checked and agreed to this agreement? The Code is as follows:

Var xieYi = document. getElementById ("xieYi ");
If (! XieYi. checked ){
Alert ("please read and check the registration agreement first! ");
Return;
}

This is the first option, but not all cases require this protocol to be checked. The protocol is sometimes not displayed on the front-end page, so the second option is changed.

The Code is as follows:

Var xieYi = document. getElementById ("xieYi ");
If (! XieYi = null &&! XieYi. checked ){
Alert ("please read and check the registration agreement first! ");
Return;
}

When xieYi does not exist, xieYi is null. When xieYi is not null and xieYi is not checked, alert is used.

Unfortunately, this code does not play the expected role.

Finally, we found that the error was caused by xieYi.

Final Version:

The Code is as follows:

Var xieYi = document. getElementById ("xieYi ");
If (xieYi! = Null &&! XieYi. checked ){
Alert ("please read and check the registration agreement first! ");
Return;
}