Question

How to create a function with an optional parameter in TypeScript

Answer 1

// TypeScript, you can create a function with an optional parameter 

// Using ? to Mark a Parameter as Optional
// Just add a ? after the parameter name.

function greet(name?: string) {
  console.log("Hello, " + (name ?? "Guest"))
}

greet("Gooz")  
greet()         



/*
run:

Hello, Gooz
Hello, Guest

*/

 

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Answer 2

// TypeScript, you can create a function with an optional parameter 

// Using Default Parameter Values

function greet(name: string = "Guest") {
  console.log("Hello, " + name)
}

greet("Luna")  
greet()       



/*
run:

Hello, Luna
Hello, Guest

*/

 

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Answer 3

// TypeScript, you can create a function with an optional parameter 

// Optional Parameters with an Options Object
// Scales when you have multiple optional values.

type GreetOptions = {
  name?: string
  shout?: boolean
}

function greet(options: GreetOptions = {}) {
  let name = options.name ?? "Guest"
  if (options.shout) {
    name = name.toUpperCase()
  }
  console.log("Hello, " + name)
}

greet()                          
greet({ name: "Vera" })         
greet({ name: "Iris ", shout: true })



/*
run:

Hello, Guest
Hello, Vera
Hello, IRIS 

*/

 

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