injectdecorator. Because decorators can't affect the type of the property they decorate, we must manually type the property. Also, we must use
declaremodifier to tell the TypeScript compiler to trust that this property will be set up by something outside this component—namely, the decorator.
ShoppingCartServicewe defined above in a component:
ShoppingCartServicein order to get any type-safety because the lookup return type is
any(see caution below).