Default Parameters in ES6

es6-default-parameter-example.js

// Default parameter syntax in ES6
// Until ES5 we were not able to declare a default value to function paramters
// ES6 gives us the liberty to do that
// Parameters value type has no restriction, it could either be an Integer or a String or an Array or even a JavaScript object

// *************************************************
// THE ES5 WAY: Let's see how we use to do it in ES5
// *************************************************/

var objAboutPerson = {
  location: {
    city: 'Kansas City',
    state: 'Missouri',
    country: 'USA'
  },
  gender: 'Male',
  age: 47,
  email: '[email protected]'
}

var arrHobby = [
  'Coding',
  'Soccer',
  'Travel',
  'Music',
  'Photography',
];

function getUser(name, role, status, objAboutPerson, arrHobby) {
  // Set default values for each parameter.
  
  name = name || '';
  role = role || 'Subsriber';
  status = status || 'Pending';
  objAboutPerson = objAboutPerson || {};
  arrHobby = arrHobby || [];
  
  console.log(name, role, status, objAboutPerson, arrHobby);
}

getUser( 'John Astor', 'Subsriber', 'Active', objAboutPerson, arrHobby );

// ****************************************************
// THE ES6 WAY: Here is how we do it with ES6
// ****************************************************/

var objAboutPerson = {
  location: {
    city: 'Kansas City',
    state: 'Missouri',
    country: 'USA'
  },
  gender: 'Male',
  age: 47,
  email: '[email protected]'
}

var arrHobby = [
  'Coding',
  'Soccer',
  'Travel',
  'Music',
  'Photography',
];

function getUser(name = '', role = 'Subscriber', status = 'Pending', objPerson = {}, arrHobby = []) {
  console.log(name, role, status, objAboutPerson, arrHobby);
}

getUser( 'John Astor', undefined, 'Active', objAbooutPerson, undefined);

// *****************************************************
// WHAT IS UNDEFINED
// *****************************************************/


// In ES6 since we have the ability to set a default value for each parameter, we also have the
// ability to "SKIP" one or more values when calling the function.
// We do this by passing 'undefined' (without quotes, as shown above). The keyword 'undefined' forces the funciton
// to use the default value of that parameter.
// It is needless to say however, the order of the values being passed must be the same the order parameters are
//  declared in the function.