Retrieves existing constructor parameters metadata and validates the given argument against their respective parameter schema

validateConstructorParams.ts

function validateConstructorParams(target: any, args: any[]) {
  // Retrieve all constructor parameters metadata
  let existingConstrainedParameters: ConstrainedParameterMap = Reflect.getOwnMetadata(
    parameterSchemaMetadataKey,
    target,
    "constructor"
  );
  // For each retrieved metadata,...
  if (existingConstrainedParameters) {
    const parameterIndexes = Object.keys(existingConstrainedParameters);
    for (let parameterIndex of parameterIndexes) {
      // Validate the argument at a given index against the relevant schema
      const { error } = existingConstrainedParameters[parameterIndex].validate(
        args[Number.parseInt(parameterIndex)]
      );
      // Bail out with an error if validation fails
      if (error instanceof Error) {
        throw error;
      }
    }
  }
}