ES6 module syntax: is it possible to `export * as Name from ...`?

Today in 2019, it is now possible.

export * as name1 from …;

The proposal for this spec has merged to ecma262. If you're looking for this functionality in an environment that is running a previous JS, there's a babel plugin for it! After configuring the plugin (or if you're using ecma262 or later), you are able to run the JS in your question:

// file: constants.js
export const SomeConstant1 = 'yay';
export const SomeConstant2 = 'yayayaya';

// file: index.js
export * as Constants from './constants.js';

// file: component.js
import { Constants } from './index.js';

const newVar = Constants.SomeConstant1; // 'yay'

No, it's not allowed in JS either, however there is a proposal to add it. For now, just use the two-step process with importing into a local variable and exporting that:

// file: constants.js
export const SomeConstant1 = 'yay';
export const SomeConstant2 = 'yayayaya';

// file: index.js
import * as Constants from './constants.js';
export {Constants};