Modern JavaScript Decorator Pattern

README.md

Modern JavaScript Decorator Pattern https://pgarciacamou.medium.com/modern-javascript-decorator-pattern-1b440500b38e

DecoratedError.js

export class DecoratedError extends Error {
  /**
   * @param {any} error
   * @param  {...Object|...() => Object} decorators
   */
  constructor(error, ...decorators) {
    if (typeof error === "string" || error instanceof String) {
      error = new Error(error);
    }

    // Decorators MUST be idempotent; no mater how many times it is executed
    // it must always return the same output, otherwise there is caos.
    //     new DecoratedError(new DecoratedError(error, decoratorA), decoratorA)
    let previouslyParsedData = {};
    if (error instanceof DecoratedError) {
      previouslyParsedData = error;
      error = error.cause;
    }

    super(error?.message, { cause: error }); // Adds stack trace
    this.decorate(defaultDecorator, previouslyParsedData, decorators);
  }

  /**
   * @throws
   * @param {...Object|...() => Object} decorators
   */
  decorate(...decorators) {
    const rawError = this.cause || {};

    while (decorators.length > 0) {
      const decorator = decorators.shift();

      // Functions are higher-order decorators that can return other decorators.
      if (decorator instanceof Function) {
        decorators.unshift(decorator(rawError, { ...this })); // prepend
        continue;
      } else if (Array.isArray(decorator)) {
        decorators = decorator.concat(decorators); // flatten & prepend
        continue;
      } else if (decorator === Object(decorator)) {
        // Filter out `undefined` properties to prevent unexpected overriding.
        for (const key in decorator) {
          if (decorator[key] !== undefined && key !== "cause") {
            // Override even non-enumerable props
            Object.defineProperty(this, key, {
              value: decorator[key],
              writable: true,
              enumerable: true,
              configurable: true
            });
          }
        }
      }
    }

    return this; // chain-of-responsibility pattern
  }
}

// This decorator could even detect complex structures.
// It doesn't have to be so simple.
function defaultDecorator(rawData, parsedData) {
  const { status, code, issue } = rawData;
  return { status, code, issue };
}