utilizing reflect-metadata to retrieve the decorators placed on an object

Question

utilizing reflect-metadata to retrieve the decorators placed on an object

There's a unique decorator in my code that seems to have no functionality:

export function myDecorator(target: any, key: string) {
   var t = Reflect.getMetadata("design:type", target, key);
}

This decorator is being used with properties of a class:

export class SomeClass {

    @globalVariable
    someProperty: string;

    @globalVariable
    fakeProperty: number;
}

What I want to achieve now is to retrieve all properties of the class that have been decorated with @globalVariable.

I attempted to use "reflect-metadata" with:

Reflect.getMetadata('globalVariable', this);

However, the result is always "undefined". Is there a way to achieve this using reflect-metadata or am I misunderstanding something?

typescript

Answer 1

Answer №1

Once a class is defined, property decorators are invoked for each property definition inside the class.

For example, if you decorate properties in SomeClass with @myDecorator:

export class SomeClass {
    @myDecorator
    someProperty: string;
}

The myDecorator function will receive:

target: (the definition of SomeClass)
key: (the name of the property)

By enabling metadata through the "emitDecoratorMetadata" property, the TypeScript compiler will produce metadata properties:

'design:type', 'design:paramtypes', and 'design:returntype'.

This enables the use of Reflect.getMetadata with these keys:

Reflect.getMetadata('design:type', ...)
Reflect.getMetadata('design:paramtypes',...)
Reflect.getMetadata('design:returntype', ...)

It's important to note that Reflect.getMetadata cannot be used with the decorator name.

Answer 2

Once a class is defined, property decorators are invoked for each property definition inside the class.

For example, if you decorate properties in SomeClass with @myDecorator:

export class SomeClass {
    @myDecorator
    someProperty: string;
}

The myDecorator function will receive:

target: (the definition of SomeClass)
key: (the name of the property)

By enabling metadata through the "emitDecoratorMetadata" property, the TypeScript compiler will produce metadata properties:

'design:type', 'design:paramtypes', and 'design:returntype'.

This enables the use of Reflect.getMetadata with these keys:

Reflect.getMetadata('design:type', ...)
Reflect.getMetadata('design:paramtypes',...)
Reflect.getMetadata('design:returntype', ...)

It's important to note that Reflect.getMetadata cannot be used with the decorator name.

Answer 3

Answer №2

To achieve the desired outcome, you must implement the globalVariable function in the following manner:

function globalVariable(target: any, propertyKey: string | Symbol): void {
    let variables = Reflect.getOwnMetadata("globalVariable", target.constructor) || [];
    variables.push(propertyKey);
    Reflect.defineMetadata("globalVariable", variables, target.constructor);
}

Then, during runtime, you will be able to invoke

Reflect.getMetadata('globalVariable', this);

as per your requirements.

Answer 4

To achieve the desired outcome, you must implement the globalVariable function in the following manner:

function globalVariable(target: any, propertyKey: string | Symbol): void {
    let variables = Reflect.getOwnMetadata("globalVariable", target.constructor) || [];
    variables.push(propertyKey);
    Reflect.defineMetadata("globalVariable", variables, target.constructor);
}

Then, during runtime, you will be able to invoke

Reflect.getMetadata('globalVariable', this);

as per your requirements.

utilizing reflect-metadata to retrieve the decorators placed on an object

Answer №1

Answer №2

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