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The future of modules
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The future of javascript modules & node
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C J Silverio CTO, @ceejbot
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you use a lot of modular javascript billions & billions of packages
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if you use code from npm the future of modules matters to you
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what's a module anyway?
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a module is a scope plus an API that lets you reuse it
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files are modules groups of files can be
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give that group of files a package.json and it's a package
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module syntax: this is what I'm sharing this is what I'm re-using
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CommonJS is one module syntax ECMAScript Modules is another
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you've seen the syntax a million times but here's a fast refresher
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const chalk = require('chalk'); // cjs import chalk from 'chalk'; // esm console.log(chalk.bold('hello world!'));
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const { yellow, bold } = require('chalk'); // cjs import { yellow, bold } from 'chalk'; // esm console.log(`${bold('hello')} ${yellow('world!')}`);
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function red(word) = { ... }; // etc module.exports = { red, green, blue, bold, ...}; // cjs export { red, green, blue, bold, ...}; // esm
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why is this worth a talk? it isn't because of syntax
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it's because the transition has not been smooth
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node needs both and it still doesn't do ESM natively
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ESM is the future of modular JavaScript
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in order to understand the future we must first understand the past
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in 2009 JS had no module spec but CommonJS had one
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there was a lot of server-side js going on and people needed a way to share code
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node adopted the CommonJS syntax and wrote a loader
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node's resolution algorithm turns a human-friendly module name into a path to code that can be loaded
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const chalk = require('chalk'); // loads './node_modules/chalk/index.js' const other = require('./chalk'); // loads './chalk.js' if it !nds it
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node's take on modules is useful you're using the heck out of it today
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browser-side js was still concatenating files
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TC39 started working on the problem in 2009
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import & export arrived in ES2015
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esm design choices differ from cjs! its intended uses are different!
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inherently asynchronous not synchronous
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(mostly) not dynamic: can't import from a variable source
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designed to support static analysis the import() variation is, however, dynamic
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see Lin Clark's cartoon deep-dive for an exploration of the details
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static analysis is important when your target is the browser
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node's nested deps are a great solution server-side, where disk space is cheap
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static analysis & tree shaking help minimize download burden in FE
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so front-end focused developers want ESM
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in between 2009 and now something very interesting happened
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node's user base changed
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throwbacks like me still write server-side js most of you use node for frontend tooling
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you didn't want to wait for new js features you wanted them now
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transpilation took off babel was the new hotness
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babel transpiled the ESM syntax into CJS and the future looked like it was here
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but babel was CJS behind the scenes which meant node's loader was doing the work
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problem: there is no esm loader
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no loader? no loader. well, html's loader.
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import {chalk} from 'https://example.com/js/chalk/index.js'; import {foo} from '../js/foo.js';
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file paths are super-predictable and super-annoying to write by hand
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node's loader is part of its magic there's no magic in spec-compliant ESM loading
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babel set some expectations for that magical resolution algorithm
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meanwhile, back in Gotham City...
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node's been using CJS for 9 years npm has 725K public packages
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you will recall, front-end dev is now what people are using node to do
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node should use JS standards when those standards exist
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therefore node should use ESM. but what does this mean?
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the devil is in the details
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ESM in node looked like it was not going good places
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very depressing talk by Myles Borins about how hard the integration was
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the systems have to co-exist but they have little in common
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how do CJS & ESM interoperate?
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can you require() an esm file? can you import a cjs file?
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how do you know which is which without parsing everything?
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node has no type="module" marker for its entry points
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so it proposed .mjs as a file suffix for javascript using the esm api
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.mjs means no parsing: every module must advertise api in name
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I'm the Stig table-flipping.
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"Well," I said. "What happens if we choose different constraints?"
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well, not very hard. Chris Dickinson & I implemented a usable take on ESM + CJS in node.
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no mjs, parse entry points; require module consumer know its api in advance
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our aim was to prove with a bit of parsing you could get a lot of usability
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reception was mixed
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technical problems are easy
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people problems are hard
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what is node for? how do we use node? where is node going?
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fundamental differences in answers lead to fundamental differences in designs
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talking thinking typing
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the node modules problem needed more talking
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I didn't want our solution adopted. I wanted the talking phase restarted.
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node has an unchartered modules team doing the hard work of talking
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it started with use cases and it's continuing with some deep questions
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see github.com/nodejs/modules to understand how complicated the tradeoffs are
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this brings us to the present state ESM is not quite there yet, but soon!
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if you are using babel in your build you have no reason not to use ESM now
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those of us not using Babel had few options until recently
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github.com/standard-things/esm
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npm init esm -y
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record scratch noise npm install -g npm@latest
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npm@6 has some goodies
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like templated init even better than npm init -y
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npm audit & npm audit !x report and automatically fix known vulnerabilities in your dep tree
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npm, Inc, is a company that sells goods and services
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you can pay us to run a very nice single-tenant registry for you
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now back to modules...
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ESM in node without a build step: npm init esm -y
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transpilation on the fly by monkey-patching the module object
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require = require('esm')(module); const Widget = require('./main.js').default; // over in main.js import fs from 'fs'; import cjs from './cjs.js'; const esm = require('./esm.js'); export default class Widget { ... }
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Q: Was that transparent interop? A: I believe it was, Bob.
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std/esm sets the tradeoff dial to max parsing for a lot of features
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is std/esm the future? not exactly. unclear where the tradeoff dial will point.
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so what is the future of modules?
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the future of node is front-end the future of node is using common standards
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learn the syntax now if you haven't yet future-you will assume ESM not CJS
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CommonJS modules won't go away you'll just use fewer of them
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migrate when you have a reason don't migrate now if you don't need to
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the future of js modules is ESM and it will be just fine
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❤ you github/ceejbot/future-of-modules