Question

How to create a function with an optional parameter in JavaScript

Answer 1

// In JavaScript, every function parameter is optional by default. 

// Default Parameter Values

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

greet("Jolie ")  
greet()         



/*
run:

Hello, Jolie 
Hello, Guest

*/

 

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Answer 2

// In JavaScript, every function parameter is optional by default. 

// Manual Check for undefined

function greet(name) {
  if (name === undefined) {
    name = "Vex"
  }
  console.log("Hello, " + name)
}

greet()
        


/*
run:

Hello, Vex

*/

 

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Answer 3

// In JavaScript, every function parameter is optional by default. 

// Optional Parameters Using nullish coalescing (??)

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

greet()      
greet(null)   
greet("Knox")  

        

/*
run:

Hello, Guest
Hello, Guest
Hello, Knox

*/

 

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Answer 4

// In JavaScript, every function parameter is optional by default. 

// Optional Parameters Using Rest Arguments (...args)

function greet(...names) {
  if (names.length === 0) {
    console.log("Hello, Guest")
  } else {
    console.log("Hello, " + names[0])
  }
}

greet()          
greet("Atlas")  

        

/*
run:

Hello, Guest
Hello, Atlas

*/

 

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Answer 5

// In JavaScript, every function parameter is optional by default. 

// Optional Parameters Using an Options Object 

function greet({ name = "Guest", shout = false } = {}) {
  if (shout) {
    name = name.toUpperCase()
  }
  console.log("Hello, " + name)
}

greet()                          
greet({ name: "Sponge" })        
greet({ name: "Bob", shout: true }) 

        

/*
run:

Hello, Guest
Hello, Sponge
Hello, BOB

*/

 

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