Add ESM Support

[evanplaice]

This PR adds preliminary ES module support with the absolute minimum changes to the existing codebase.

Changes:

• adds a second grunt-concat aliases to concat_esm
• removed the traditional loaders.js from the .esm.js config to avoid conflicts with module.exports
• assigns the IIFE to a variable and assigns it to the default export
• removes the this binding to global scope, ESM enforces strict mode by default so binding to global this is not allowed.
• generated new dist files
• added 'grunt build-esm' to trigger the build
• add grunt build-esm to the prerelease steps

Usage

This assumes the module is being used in a browser (ie hence no bare import specifier) that includes ESM support.

import Showdown from '/node_modules/showdown/dist/showdown.esm.js';

const raw = '' // <- assume some raw markdown here
const md = new Showdown.Converter().makeHtml(raw);
document.getElementById('some-element').innerHTML = md;

Ref: #660

[evanplaice]

Note: Changed extension from .mjs to .esm.js. Even in Node .mjs is no longer required to use ECMAScript modules.

BTW. Feedback is welcome on this. I know it's not a part of the existing roadmap. I will own whatever additional work is necessary to make this acceptable.

[Marshal27]

It's unfortunate this wasn't consumed... maybe there is a legitimate reason by the maintainers I haven't been able to find?

Regardless, I have an Open-Wc lerna repo that is a pure ES build pipeline and received a feature request to parse HTML to markdown and vice versa... there are not any ES libraries that can do bi-directional; your dist in this PR helped me out a lot and I thank you for doing this work... so far works wonderfully to solve my issue!

[mansona]

Hey @evanplaice 👋 just curious why you closed this PR? I know it was open for a little while but I wonder if we should open it again to help try to get it merged. What do you think?

[evanplaice]

This PR sat for more than a year without a response from the Maintainers

As an Author, Maintainer, and Contributor of many many projects; tracking the status of a single PR that sat untouched for >1 year isn't really a good use of my time.

The minimal set of changes required to convert Showdown to ESM are available in this PR. Showdown's Maintainers can always pick up where I left off if they decide to make the change. I just did the work so if/when they decide to make the switch, it'll be an easy transition.

In that regard. Please do not ping me again from this project unless you are an active Maintainer.