"destructuring + restructuring": merging objects with defaults using destructuring instead of `extend(..)`

1.js

// most common approach, using extend(..)

var defaults = {
  url: "http://some.base.url/api",
  method: "post",
  headers: [
    "Content-Type: text/plain"
  ]
};

console.log(defaults);

// ************************

var settings = {
  url: "http://some.other.url/",
  data: 42,
  callback: function(resp) { /* .. */ }
};

// underscore extend(..)
ajax( _.extend({},defaults,settings) );

// or: ajax( Object.assign({},defaults,settings) );

2.js

// instead, IMO better using destructuring and defaults

var defaults = ajaxOptions();  // with no arguments, returns the defaults as an object if necessary

console.log(defaults);

// ************************

var settings = {
  url: "http://some.other.url/",
  data: 42,
  callback: function(resp) { /* .. */ }
};

ajax( ajaxOptions( settings ) );  // with an argument, mixes in the settings w/ the defaults

// ************************

function ajaxOptions({
   url = "http://some.base.url/api",
   method = "post",
   data,
   callback,
   headers: [
     headers0 = "Content-Type: text/plain",
     ...otherHeaders
   ] = []
} = {}) {
   return {
     url, method, data, callback,
     headers: [
       headers0,
       ...otherHeaders
     ]
   };
}