javascript - Can't use new ecmascript decorators in typescript 2.4.2 -


here code example:

function enumerable(value: boolean) {   return function (target: any, propertykey: string, descriptor: propertydescriptor) {     descriptor.enumerable = value;   }; }  class {   @enumerable(false)   a: number = 1   b: number = 2    mymethod () {} }  const = new a()

whatever try get:

d:(real path removed)/first-try-typescript>tsc --emitdecoratormetadata --experimentaldecorators decorators.ts decorators.ts(8,3): error ts1240: unable resolve signature of property decorator when called expression.

i have tried same stackoferflow questions suggestions:

  • adding emitdecoratormetadata & experimentaldecorators tsconfig
  • running tsc --emitdecoratormetadata --experimentaldecorators
  • adding :any mark decorator function returning value
  • adding descriptor: typedpropertydescriptor<any> type

i error. both in terminal , in webstorm code hints. method decorator - same thing (see example below).

function test(target: object,               propertykey: string,               descriptor: typedpropertydescriptor<any>): {   return descriptor; }  class {   a: number = 1   b: number = 2    @test   mymethod () {} }  const = new a()

up date code here - https://github.com/rantiev/first-try-typescript

unfortunately, property decorators not have access property descriptor, properties live on class instance, while decorators evaluated before instance possibly exist. also, can use following signature property decorator:

function (target: any, propkey: string | symbol)

so no descriptor here.

you can't object.defineproperty(target, propkey.tostring, { enumerable: false, value: ... }) because shared across instances of class, i.e. setting property in 1 instance leak another.

achieving doing possible though, bit complicated. create getter on prototype creates desired property descriptor in time. like:

function enumerable(value: boolean) {     return function (target: any, propkey: string | symbol) {         object.defineproperty(target, propkey, {             get: function () {                 // in here, 'this' refer class instance.                 object.defineproperty(this, propkey.tostring(), {                     value: undefined,                     enumerable: value                 });             },             set: function (setvalue: any) {                 // in here, 'this' refer class instance.                 object.defineproperty(this, propkey.tostring(), {                     value: setvalue,                     enumerable: value                 });             }         });     }; }

the "outer" get/set functionality run once, instance property shadow after property descriptor has been created on instance.


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