In some scenarios, we may want to pass values only for minimal parameters. In such cases, we can define the properties in an interface as optional properties, as follows:

interface Customer { 
  id: number; 
  name: string; 
  bonus?: number; 
}  
function addCustomer(customer: Customer) {  
  if (customer.bonus) { 
    console.log(customer.bonus); 
  } 
}  
addCustomer({id: 101, name: "Rajesh Gunasundaram"}); 

Here, the bonus property has been defined as an optional property by concatenating a question mark (?) at the end of the name property.