ES6 Object.assign( target, source ) as a native options object merging pattern.

options-objects.js

let defaults  = { file: null };

function foo(options) {
    // Merging defaults and options objects in ES6
    options = [ defaults, options ].reduce(Object.assign, {});
}


foo({ file: "happy.md" });


/* 

Object.assign( target, source )

When passed as the callback to reduce, the params are bound as:

function( prev, value ) {}

*/

spec.md

Object.assign( target, source )

Object.assign( target, source )

Rough spec expectations:

• Only enumerable own properties of source
• Invoke [[Get]] on property list derived from source, for each property in list [[Put]] on target
• private names are not copied
• unique names are copied
• super mechanism (rebind super)… AWB To determine needs
• Returns modified "target"

Wouldn't this make more sense: (I might be late to this discussion)
constructor({opt1, opt2, opt3} = {opt1: def1, opt2: def2, opt3: def3}) { ... }