ECMAScript object spread/rest – assigning to multiple properties at once

The new object rest/spread syntax has some surprisingly nice applications, like omitting a field from an object.

Is there a (proposed) way to also assign to several properties of an object, the values from variables with the same names? In other words, a shorter way to say:

o.foo = foo;
o.bar = bar;
o.baz = baz;

Note: Without losing the existing properties of o, only adding to them.

Answer

Use Object.assign:

const o = { initial: 'initial' };
const foo = 'foo';
const bar = 'bar';
const baz = 'baz';
Object.assign(o, { foo, bar, baz });
console.log(o);

Note that both shorthand property names and Object.assign were introduced in ES6 – it’s not something that requires an extremely up-to-date browser/environment.

Something similar that reassigns the reference to the object would be to initialize another object by spreading o and list foo, bar, baz:

let o = { initial: 'initial' };
const foo = 'foo';
const bar = 'bar';
const baz = 'baz';

o = { ...o, foo, bar, baz };
console.log(o);