useClass expects a type name and Angular creates an instance from the passed type and also resolves and passes constructor parameters to the class if there are any. There is also useExisting which is like an alias for an already registered provider.

What is multi true in Angular?

multi: true means that one provider token provides an array of elements. For example all directives for router support routerLink , router-outlet are provided by ROUTER_DIRECTIVES . If a new provider is registered with the token ROUTER_DIRECTIVES , then it overrides the previously registered directives.

What is DI token in Angular?

The DI system in Angular uses tokens to uniquely identify a Provider. There are three types of tokens that you can create in Angular. They are Type Token, String Token, and Injection Token. DI Tokens.