Return Lastname when not definded-CodePudding

I'm studying JavaScript combining functions. Supposed I have firstname and lastName as two arguments of my function. I want the console to display Doe when lastname is undefinded . Here is my code but it printed out undefined. Any idea? Thank you!

let name = 'John'

function greetByDefault(firstname,lastname){
     return 'Hi '   firstname  ' '  lastname   '!';
 }
  if (lastname === undefined){
        return 'Doe';
 }

console.log(greetByDefault('Jane', 'Doe'));
console.log(greetByDefault(name));

I want the console output to be:

Hi Jane Doe! Hi John Doe!

CodePudding user response：

you can do something like this using a default value

let name = 'John'

function greetByDefault(firstname,lastname = 'Doe'){
     return 'Hi '   firstname  ' '  lastname   '!';
 }
 

console.log(greetByDefault('Jane', 'Doe'));
console.log(greetByDefault(name));
console.log(greetByDefault(name, 'Smith'))

CodePudding user response：

You have to put everything in function

let name = 'John'
function greetByDefault(firstname,lastname){
  if (lastname === undefined){
      lastname = 'Doe';
  }
     return 'Hi '   firstname  ' '  lastname   '!';
 }

console.log(greetByDefault('Jane', 'Doe'));
console.log(greetByDefault(name));

CodePudding user response：

let name = 'John'
function greetByDefault(firstname,lastname=''){
 if (lastname== ''){
    lastname =  'Doe';
  }
return 'Hi '   firstname  ' '  lastname   '!';

}
console.log(greetByDefault('Jane', 'Doe'));
console.log(greetByDefault(name));