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Yosuke Furukawa
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April 24, 2018
Programming
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mjs
We are JavaScripters で発表した .mjs の話です。
Yosuke Furukawa
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April 24, 2018
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Transcript
.mjs 2018/04/24 We are JavaScripters!! @ Recruit Technologies
Twitter: @yosuke_furukawa Github: yosuke-furukawa
Node.js v10 Release (maybe tomorrow)
Node.js v10 Notable Changes • for-await-of in Stream experimental
support • ESModules experimental support • private/public class fields experimental support • fs/promises
DEMO
DEMO import fs from 'fs/promises'; import util from 'util'; async
function main() { try { const content = await fs.readFile(process.argv[2]) console.log(content.toString()) } catch(e) { console.error(e.toString()); } } main();
file name is … foo.mjs
ʊʊਓਓਓʊʊ ʼɹ.mjs !!!ɹʻ ʉʉY^Y^Yʉʉ
Yes, we have long discussion about ESM.
We need ".mjs".
Why?
Module !== Script
Module [ "strict", "top level scope", "reserved await" ] Script
[ "non strict", "global scope", ]
We need to detect which mode on load file.
if file.lastIndexOf(".mjs") { Module } else { Script }
Simple and Faster
We do not use ".js" ???? (´ɾωɾʆ)
No, 2 reasons.
Use loader option.
DEMO
DEMO const builtins = Module.builtinModules; const URL = url.URL; const
baseURL = new URL('file://'); baseURL.pathname = `${process.cwd()}/`; export function resolve(specifier, parentModuleURL = baseURL, defaultResolve) { if (builtins.includes(specifier)) { return { url: specifier, format: 'builtin' }; } const resolved = new url.URL(specifier, parentModuleURL); const ext = path.extname(resolved.pathname); return { url: resolved.href, format: 'esm' }; }
DEMO $ node —experimental-modules —loader loader.mjs file.js // file.js import
fs from 'fs'; import util from 'util'; const readFile = util.promisify(fs.readFile); async function main() { try { const content = await readFile(process.argv[2]) console.log(content.toString()) } catch(e) { console.error(e.toString()); } } main();
mode detection on flag `—mode` , package.json see: https://gist.github.com/ceejbot/b49f8789b2ab6b09548ccb72813a1054
https://docs.google.com/presentation/d/ 1xK1ana_TIxfAHX33CYVHFnJsV0If_YirLtRBBga9cv0/edit#slide=id.p
You just use ".js" if you don’t need to use
ESM.
You would be better to use ".mjs", if you need
ESM on Node.js v9-10.
You would be better to wait the conclusion, if you
want to use ES Modules in the future.
ऄ (da-soku) +
Filename Extensions YOMO-YAMA
Long long time ago… Brendan Eich saids …
)PXEPXFUIJOLFT FTpMFFYUFOTJPOTUPEFUFDU WFSTJPOT // sorry no reference… I cannot find
link 8FOFFEUPDIBOHFpMFOBNFFYUFOTJPOTUPVQHSBEF UIBUJTOJHIUNBSFʜ
*EJTMJLFNPEFT8IPEPFTOU #VUUIJTTPVOETMJLF UIF7FSTJPOJOHJTBOBOUJQBUUFSOTIJCCPMFUI*WF IFBSESFDFOUMZSF8FC4PDLFUT*UEPFTOPUSFqFDU SFBMJUZ https://esdiscuss.org/topic/no-more-modes 3FDFOUMZ *NFUXJUIUIF(PPHMF7UFBNGPSUXPGVMM EBZT0OFNFTTBHFUIBUDBNFUISPVHIMPVEBOE DMFBS
UIBU*TBJE*XPVMESFMBZUPUIFMJTU JTQMFBTF OPNPSFNPEFT
Web does not have version/mode.
All we need is feature detection.
Detectable Feature // Feature Detection if (!Array.isArray) {} if (!String.prototype.trimStart)
{}
un-detectable feature (on runtime) class A {} import / export
#foo // syntax
Modern JavaScript is difficult to detect features.
Module JavaScript is JavaScript 2.0
JavaScript is not so easy, We are JavaScripters, Every JSers
would be better to enjoy chaos.
Enjoy JS Chaos :)
Thanks