(Newbie) Why can a function be defined in json object? : I am reading a React doc, https://reacttraining.com/react-router/web/example/auth-workflow, and trying to understand the following piece of code:

Looks like a the function definition happens in a json object, but my understanding is that we can't have funciton inside json 
     
       const fakeAuth = {
          isAuthenticated: false,
          authenticate(cb) {
            this.isAuthenticated = true;
            setTimeout(cb, 100); // fake async
          },
          signout(cb) {
            this.isAuthenticated = false;
            setTimeout(cb, 100);
          }
        };