Discovering the names of parameters when using decorators

Question

Discovering the names of parameters when using decorators

I am in the process of creating a decorator to verify the validity of certain parameters.

Below is the method I am working on,

getUsers(offset, limit, orderBy, sort){
....
}

I want to ensure that the value of orderBy is either 'createdAt' or 'updatedAt'; otherwise, an HTTP response will be returned.

Similarly, for the sort parameter, it should only be 'ASC' or 'DESC'.

Therefore, I am looking for a way to utilize a decorator to streamline this validation process and make my code more concise. Currently, I have the following block of code to perform these checks:

if (!includes(this.orderByFields, orderBy)) {
  return Utils.HttpError.badRequest(`You are allowed to order by [ ${this.orderByFields.join(', ')} ] only.`);
}

If you have any suggestions on how to achieve this using decorators, that would be greatly appreciated. Thank you in advance :-)

javascript typescript decorator

Answer 1

Answer №1

You can implement a function like the following:

type ApiFunction = (offset: number, limit: number, orderBy: string, sort: string) => any;

const orderByFields = ["createdAt", "updatedAt"];
function validateRequest() {
  return function(_target: any, _propertyName: string, descriptor: TypedPropertyDescriptor<ApiFunction>) {
    const originalMethod = descriptor.value!;
    descriptor.value = function(offset, limit, orderBy, sort) {
      if (!orderByFields.includes(orderBy)) {
        return "Bad Request";
      }
      return originalMethod.bind(this)(offset, limit, orderBy, sort);
    };
  };
}

This approach ensures that the decorator is only applied to methods with a specific signature.

For instance, you can use it as shown below:

class Foo {
  @validateRequest()
  getUsers(offset: number, limit: number, orderBy: string, sort: string): string {
    return "Result";
  }
}

In addition, consider enforcing parameter types on the type-level for orderBy and sort. If you are the sole consumer of this API, decorators may not be necessary:

function getUsers(offset: number, limit: number, orderBy: "createdAt" | "updatedAt", sort: "ASC" | "DESC") {}

Answer 2

You can implement a function like the following:

type ApiFunction = (offset: number, limit: number, orderBy: string, sort: string) => any;

const orderByFields = ["createdAt", "updatedAt"];
function validateRequest() {
  return function(_target: any, _propertyName: string, descriptor: TypedPropertyDescriptor<ApiFunction>) {
    const originalMethod = descriptor.value!;
    descriptor.value = function(offset, limit, orderBy, sort) {
      if (!orderByFields.includes(orderBy)) {
        return "Bad Request";
      }
      return originalMethod.bind(this)(offset, limit, orderBy, sort);
    };
  };
}

This approach ensures that the decorator is only applied to methods with a specific signature.

For instance, you can use it as shown below:

class Foo {
  @validateRequest()
  getUsers(offset: number, limit: number, orderBy: string, sort: string): string {
    return "Result";
  }
}

In addition, consider enforcing parameter types on the type-level for orderBy and sort. If you are the sole consumer of this API, decorators may not be necessary:

function getUsers(offset: number, limit: number, orderBy: "createdAt" | "updatedAt", sort: "ASC" | "DESC") {}

Discovering the names of parameters when using decorators

Answer №1

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