JS: Object.assign

New in ES2015.

Object.assign ( target_obj, source_obj_1, source_obj_2, … )

Shallow copy the values of all of the enumerable own properties from source_obj_1, source_obj_2 etc objects to a target_obj object.

[see JS: Property Attributes, writable, enumerable, configurable]

Return the modified target_obj.

target_obj is modified.

const A = {a1: 3};
const B = {b1: 3};
const T = {};

// add properties from A and B to T. Returns the new T
console.log ( Object.assign ( T, A, B ) ); // { a1: 3, b1: 3 }

// value of variable T is changed
console.log ( T ); // { a1: 3, b1: 3 }

const x1 = {a1: 4};
const x2 = {a1: 3};

// if properties are same, value is overwritten
console.log ( Object.assign ( x2, x1 ) ); // { a1: 4 }

Reference

ECMAScript® 2016 Language Specification#sec-object.assign