default functions javascript 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 parameter default parameter

function say(message='Hi') {
    console.log(message);
}
say(); // 'Hi'
say(undefined); // 'Hi'
say('Hello'); // 'Hello'


function date(d = today()) {
    console.log(d);
}
function today() {
    return (new Date()).toLocaleDateString("en-US");
}
date();


function add(x = 1, y = x, z = x + y) {
    return x + y + z;
}
console.log(add()); // 4