you can use optional variable by ? or if you have multiple optional variable by ..., example:

function details(Name: string, country="CA", address?: string, ...hobbies: string) { // ... } 

In the above: Name: is a must country: has a default address: is an optional param hobbies: is an array of optional params

you can use optional variable by ? or if you have multiple optional variable by ..., example:

function details(name: string, country="CA", address?: string, ...hobbies: string) { // ... } 

In the above: 

• name is required
• country is required and has a default value
• address is optional
• hobbies is an array of optional params