Global routing front guard (beforeEach) This function is used the most. Its function is to perform permission-related verification before routing jumps. This function contains three parameters: to: the object of the target route that is about to enter; from: the route that the current route is leaving; next: confirm the release. It can be used to log in and register, to determine whether there is a token before logging in, and release if it exists. , if it does not exist, it will not be released. The post routing guard (afterEach), its role is to trigger after the routing jump.