Universal decorator factories made from scratch
yarn add @qiwi/decorator-utils- There's no right way to support both decorator types: with
@parentheses()and@plain. Holy War thread: wycats/javascript-decorators/issues/23 - TypeScript 5 decorators: announcing-typescript-5-0, TS/issues/52435, nestjs/issues/10959
- TC39 stage-3 proposal decorators
import {constructDecorator} from '@qiwi/decorator-utils'
const decorator = constructDecorator((targetType, target, param) => {
if (targetType === METHOD) {
return value => param || 'qux'
}
})
class Foo {
@decorator()
foo () { return 'bar' }
@decorator('BAZ')
baz () { return 'baz' }
}const decorator = constructDecorator((targetType, target) => {
if (targetType === CLASS) {
return class Bar extends target {
constructor (name, age) {
super(name)
this.age = age
}
}
}
})
@decorator()
class Foo {
constructor (name) {
this.name = name
}
foo () { return 'bar' }
}import {createDecorator, FIELD, PARAM} from '@qiwi/decorator-utils'
const meta: any = {}
const decorator = constructDecorator(({
propName,
paramIndex,
targetType,
target,
args: [param]
}: IDecoratorHandlerContext) => {
if (targetType === PARAM) {
if (propName && typeof paramIndex === 'number') {
meta[propName] = meta[propName] || {}
meta[propName][paramIndex] = target
}
}
if (targetType === FIELD) {
if (propName) {
meta[propName] = param
}
}
})
class Foo {
@decorator('arg')
foo = 'bar'
bar(one: any, @decorator() two: any) {
return 'bar'
}
}
/**
Now `meta` is smth like:
{
foo: 'arg',
bar: {
1: Foo.prototype.bar,
},
}
*/You may also apply the decorator to the class, but decorate its methods:
const decorator = constructDecorator((targetType, target) => {
if (targetType === METHOD) {
return () => {
return target().toUpperCase()
}
}
})
@decorator()
class Foo {
foo () { return 'bar' }
baz () { return 'baz' }
}constructDecorator factory provides the handler access to the decorator context.
This data describes the specifics of the decorated target, decorator arguments and so on.
type IDecoratorHandlerContext = {
args: IDecoratorArgs
kind: ITargetType | null // targetType alias
targetType: ITargetType | null
target: ITarget
proto: IProto
ctor: Function
name?: IPropName // propName alias
propName?: IPropName
paramIndex?: IParamIndex
descriptor?: IDescriptor
}You may set additional options to apply some decorator asserts: allowed target types, repeatable or not.
const plus = constructDecorator(
({ targetType, target, args: [param] }) => {
return (value: number) => target(value) + param
},
{
allowedTypes: METHOD, // string | string[]
repeatable: true,
},
)
class Foo {
@plus(2)
@plus(1)
bar(v: number) {
return v
}
}If the global Reflect provides getMetadataKeys, getMetadata and defineMetadata methods, they will be used to attach corresponding data to the decorated targets.
To enable, just add reflect-metadata to your dependencies and load it.
import 'reflect-metadata'
import {constructDecorator} from '@qiwi/decorator-utils'
// ...