https://babeljs.io/docs/en/babel-plugin-proposal-decorators

.babelrc

{
  "plugins": [["@babel/plugin-proposal-decorators", { "version": "2021-12" }]]
}

README.md

decoratorをbabelしてみる

パッケージのインストール

npm install -D@babel/cli @babel/core @babel/plugin-proposal-decorators

実行コマンド

babel before.js

after.js

var _initClass;

function createMetadataMethodsForProperty(metadataMap, kind, property, decoratorFinishedRef) { return { getMetadata: function (key) { assertNotFinished(decoratorFinishedRef, "getMetadata"), assertMetadataKey(key); var metadataForKey = metadataMap[key]; if (void 0 !== metadataForKey) if (1 === kind) { var pub = metadataForKey.public; if (void 0 !== pub) return pub[property]; } else if (2 === kind) { var priv = metadataForKey.private; if (void 0 !== priv) return priv.get(property); } else if (Object.hasOwnProperty.call(metadataForKey, "constructor")) return metadataForKey.constructor; }, setMetadata: function (key, value) { assertNotFinished(decoratorFinishedRef, "setMetadata"), assertMetadataKey(key); var metadataForKey = metadataMap[key]; if (void 0 === metadataForKey && (metadataForKey = metadataMap[key] = {}), 1 === kind) { var pub = metadataForKey.public; void 0 === pub && (pub = metadataForKey.public = {}), pub[property] = value; } else if (2 === kind) { var priv = metadataForKey.priv; void 0 === priv && (priv = metadataForKey.private = new Map()), priv.set(property, value); } else metadataForKey.constructor = value; } }; }

function convertMetadataMapToFinal(obj, metadataMap) { var parentMetadataMap = obj[Symbol.metadata || Symbol.for("Symbol.metadata")], metadataKeys = Object.getOwnPropertySymbols(metadataMap); if (0 !== metadataKeys.length) { for (var i = 0; i < metadataKeys.length; i++) { var key = metadataKeys[i], metaForKey = metadataMap[key], parentMetaForKey = parentMetadataMap ? parentMetadataMap[key] : null, pub = metaForKey.public, parentPub = parentMetaForKey ? parentMetaForKey.public : null; pub && parentPub && Object.setPrototypeOf(pub, parentPub); var priv = metaForKey.private; if (priv) { var privArr = Array.from(priv.values()), parentPriv = parentMetaForKey ? parentMetaForKey.private : null; parentPriv && (privArr = privArr.concat(parentPriv)), metaForKey.private = privArr; } parentMetaForKey && Object.setPrototypeOf(metaForKey, parentMetaForKey); } parentMetadataMap && Object.setPrototypeOf(metadataMap, parentMetadataMap), obj[Symbol.metadata || Symbol.for("Symbol.metadata")] = metadataMap; } }

function createAddInitializerMethod(initializers, decoratorFinishedRef) { return function (initializer) { assertNotFinished(decoratorFinishedRef, "addInitializer"), assertCallable(initializer, "An initializer"), initializers.push(initializer); }; }

function memberDec(dec, name, desc, metadataMap, initializers, kind, isStatic, isPrivate, value) { var kindStr; switch (kind) { case 1: kindStr = "accessor"; break; case 2: kindStr = "method"; break; case 3: kindStr = "getter"; break; case 4: kindStr = "setter"; break; default: kindStr = "field"; } var metadataKind, metadataName, ctx = { kind: kindStr, name: isPrivate ? "#" + name : name, isStatic: isStatic, isPrivate: isPrivate }, decoratorFinishedRef = { v: !1 }; if (0 !== kind && (ctx.addInitializer = createAddInitializerMethod(initializers, decoratorFinishedRef)), isPrivate) { metadataKind = 2, metadataName = Symbol(name); var access = {}; 0 === kind ? (access.get = desc.get, access.set = desc.set) : 2 === kind ? access.get = function () { return desc.value; } : (1 !== kind && 3 !== kind || (access.get = function () { return desc.get.call(this); }), 1 !== kind && 4 !== kind || (access.set = function (v) { desc.set.call(this, v); })), ctx.access = access; } else metadataKind = 1, metadataName = name; try { return dec(value, Object.assign(ctx, createMetadataMethodsForProperty(metadataMap, metadataKind, metadataName, decoratorFinishedRef))); } finally { decoratorFinishedRef.v = !0; } }

function assertNotFinished(decoratorFinishedRef, fnName) { if (decoratorFinishedRef.v) throw new Error("attempted to call " + fnName + " after decoration was finished"); }

function assertMetadataKey(key) { if ("symbol" != typeof key) throw new TypeError("Metadata keys must be symbols, received: " + key); }

function assertCallable(fn, hint) { if ("function" != typeof fn) throw new TypeError(hint + " must be a function"); }

function assertValidReturnValue(kind, value) { var type = typeof value; if (1 === kind) { if ("object" !== type || null === value) throw new TypeError("accessor decorators must return an object with get, set, or init properties or void 0"); void 0 !== value.get && assertCallable(value.get, "accessor.get"), void 0 !== value.set && assertCallable(value.set, "accessor.set"), void 0 !== value.init && assertCallable(value.init, "accessor.init"), void 0 !== value.initializer && assertCallable(value.initializer, "accessor.initializer"); } else if ("function" !== type) { var hint; throw hint = 0 === kind ? "field" : 10 === kind ? "class" : "method", new TypeError(hint + " decorators must return a function or void 0"); } }

function getInit(desc) { var initializer; return null == (initializer = desc.init) && (initializer = desc.initializer) && "undefined" != typeof console && console.warn(".initializer has been renamed to .init as of March 2022"), initializer; }

function applyMemberDec(ret, base, decInfo, name, kind, isStatic, isPrivate, metadataMap, initializers) { var desc, initializer, value, newValue, get, set, decs = decInfo[0]; if (isPrivate ? desc = 0 === kind || 1 === kind ? { get: decInfo[3], set: decInfo[4] } : 3 === kind ? { get: decInfo[3] } : 4 === kind ? { set: decInfo[3] } : { value: decInfo[3] } : 0 !== kind && (desc = Object.getOwnPropertyDescriptor(base, name)), 1 === kind ? value = { get: desc.get, set: desc.set } : 2 === kind ? value = desc.value : 3 === kind ? value = desc.get : 4 === kind && (value = desc.set), "function" == typeof decs) void 0 !== (newValue = memberDec(decs, name, desc, metadataMap, initializers, kind, isStatic, isPrivate, value)) && (assertValidReturnValue(kind, newValue), 0 === kind ? initializer = newValue : 1 === kind ? (initializer = getInit(newValue), get = newValue.get || value.get, set = newValue.set || value.set, value = { get: get, set: set }) : value = newValue);else for (var i = decs.length - 1; i >= 0; i--) { var newInit; if (void 0 !== (newValue = memberDec(decs[i], name, desc, metadataMap, initializers, kind, isStatic, isPrivate, value))) assertValidReturnValue(kind, newValue), 0 === kind ? newInit = newValue : 1 === kind ? (newInit = getInit(newValue), get = newValue.get || value.get, set = newValue.set || value.set, value = { get: get, set: set }) : value = newValue, void 0 !== newInit && (void 0 === initializer ? initializer = newInit : "function" == typeof initializer ? initializer = [initializer, newInit] : initializer.push(newInit)); } if (0 === kind || 1 === kind) { if (void 0 === initializer) initializer = function (instance, init) { return init; };else if ("function" != typeof initializer) { var ownInitializers = initializer; initializer = function (instance, init) { for (var value = init, i = 0; i < ownInitializers.length; i++) value = ownInitializers[i].call(instance, value); return value; }; } else { var originalInitializer = initializer; initializer = function (instance, init) { return originalInitializer.call(instance, init); }; } ret.push(initializer); } 0 !== kind && (1 === kind ? (desc.get = value.get, desc.set = value.set) : 2 === kind ? desc.value = value : 3 === kind ? desc.get = value : 4 === kind && (desc.set = value), isPrivate ? 1 === kind ? (ret.push(function (instance, args) { return value.get.call(instance, args); }), ret.push(function (instance, args) { return value.set.call(instance, args); })) : 2 === kind ? ret.push(value) : ret.push(function (instance, args) { return value.call(instance, args); }) : Object.defineProperty(base, name, desc)); }

function applyMemberDecs(ret, Class, protoMetadataMap, staticMetadataMap, decInfos) { for (var protoInitializers, staticInitializers, existingProtoNonFields = new Map(), existingStaticNonFields = new Map(), i = 0; i < decInfos.length; i++) { var decInfo = decInfos[i]; if (Array.isArray(decInfo)) { var base, metadataMap, initializers, kind = decInfo[1], name = decInfo[2], isPrivate = decInfo.length > 3, isStatic = kind >= 5; if (isStatic ? (base = Class, metadataMap = staticMetadataMap, 0 !== (kind -= 5) && (initializers = staticInitializers = staticInitializers || [])) : (base = Class.prototype, metadataMap = protoMetadataMap, 0 !== kind && (initializers = protoInitializers = protoInitializers || [])), 0 !== kind && !isPrivate) { var existingNonFields = isStatic ? existingStaticNonFields : existingProtoNonFields, existingKind = existingNonFields.get(name) || 0; if (!0 === existingKind || 3 === existingKind && 4 !== kind || 4 === existingKind && 3 !== kind) throw new Error("Attempted to decorate a public method/accessor that has the same name as a previously decorated public method/accessor. This is not currently supported by the decorators plugin. Property name was: " + name); !existingKind && kind > 2 ? existingNonFields.set(name, kind) : existingNonFields.set(name, !0); } applyMemberDec(ret, base, decInfo, name, kind, isStatic, isPrivate, metadataMap, initializers); } } pushInitializers(ret, protoInitializers), pushInitializers(ret, staticInitializers); }

function pushInitializers(ret, initializers) { initializers && ret.push(function (instance) { for (var i = 0; i < initializers.length; i++) initializers[i].call(instance); return instance; }); }

function applyClassDecs(ret, targetClass, metadataMap, classDecs) { if (classDecs.length > 0) { for (var initializers = [], newClass = targetClass, name = targetClass.name, i = classDecs.length - 1; i >= 0; i--) { var decoratorFinishedRef = { v: !1 }; try { var ctx = Object.assign({ kind: "class", name: name, addInitializer: createAddInitializerMethod(initializers, decoratorFinishedRef) }, createMetadataMethodsForProperty(metadataMap, 0, name, decoratorFinishedRef)), nextNewClass = classDecs[i](newClass, ctx); } finally { decoratorFinishedRef.v = !0; } void 0 !== nextNewClass && (assertValidReturnValue(10, nextNewClass), newClass = nextNewClass); } ret.push(newClass, function () { for (var i = 0; i < initializers.length; i++) initializers[i].call(newClass); }); } }

function _applyDecs(targetClass, memberDecs, classDecs) { var ret = [], staticMetadataMap = {}, protoMetadataMap = {}; return applyMemberDecs(ret, targetClass, protoMetadataMap, staticMetadataMap, memberDecs), convertMetadataMapToFinal(targetClass.prototype, protoMetadataMap), applyClassDecs(ret, targetClass, staticMetadataMap, classDecs), convertMetadataMapToFinal(targetClass, staticMetadataMap), ret; }

let _MyClass;

class MyClass {
  static {
    [_MyClass, _initClass] = _applyDecs(this, [], [annotation]);
  }
  static {
    _initClass();

  }
}

function annotation(target) {
  target.annotated = true;
}

before.js

@annotation
class MyClass {}

function annotation(target) {
  target.annotated = true;
}