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.

Return the modified target_obj.

target_obj is modified.

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

// add properties form 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 }

Reference

ECMAScript® 2016 Language Specification#sec-object.assign