how to add a default value to an perameter in js code example

Example 1: javascript constructor default parameter

function greet(name, greeting, message = greeting + ' ' + name) {
  return [name, greeting, message]
}

greet('David', 'Hi')                     // ["David", "Hi", "Hi David"]
greet('David', 'Hi', 'Happy Birthday!')  // ["David", "Hi", "Happy Birthday!"]

Example 2: javascript default parameters

function multiply(a, b = 1) {
  return a * b;
}