Adding -mjs.js build to support polymer-cli

[cloudily]

No description provided.

[coveralls]

Coverage remained the same at 94.309% when pulling 151b745 on cloudily:feature-polyer_cli_support_for_mjs into f67d5c2 on pladaria:master.

[pladaria]

Hi, thank you for this PR

Before accepting it I need some more context. Why do you need this?

How does polymer-cli know about the newly created artifact? It is not listed in package.json.
It is this following some kind of naming convention?

Thanks

[cloudily]

Hi @pladaria,

The mjs extension has not been formalized yet. It is currently recognized by node, but not by some build tools. For example, the polymer-cli throws an error with the unrecognized mjs extension. This is to provide build tools a way to interpret these files as they relate to ES imports. Please let me know if you have any further questions.

When importing into the frontend, we use the following syntax:

import ReconnectingWebSocket from 'reconnecting-websocket/dist/reconnecting-websocket.mjs';

This currently fails build tools because of the mjs extension, hence the addition. I didn't want to change it for everyone, as it would be a breaking change.

[pladaria]

All clear! Thank you for your explanation

[pladaria]

published 4.1.10 with that change

[cloudily]

Thanks, @pladaria