decorators.ts

import 'reflect-metadata';

import AWS from 'aws-sdk';

const metadataKey = Symbol('snsAttribute');

function snsAttribute(isSnsAttribute: boolean = true) {
  return Reflect.metadata(metadataKey, isSnsAttribute);
}


class Alex {
  public x: string;

  @snsAttribute()
  public y: string;
}

const a = new Alex();

a.x = 'x';
a.y = 'why';

function hasSnsAttribute(target: any, propertyKey: string) {
  return Reflect.getMetadata(metadataKey, target, propertyKey);
}

const attrs = Object.entries(a).reduce(
  (previousValue: AWS.SNS.MessageAttributeMap, currentValue: [string, any]) => {
    const [key, value] = currentValue;

    if (hasSnsAttribute(a, key)) {
      const attribute: AWS.SNS.MessageAttributeValue = {
        DataType: 'String',
        StringValue: value,
      };

      return Object.assign(previousValue, {
        [key]: attribute,
      });
    }

    return previousValue;
  },
  {} as AWS.SNS.MessageAttributeMap,
);

console.dir(attrs);