deprecate.ts

//copied from https://github.com/jayphelps/core-decorators

const { defineProperty, getOwnPropertyDescriptor,
  getOwnPropertyNames, getOwnPropertySymbols } = Object;

export function isDescriptor(desc) {
  if (!desc || !desc.hasOwnProperty) {
    return false;
  }

  const keys = ['value', 'initializer', 'get', 'set'];

  for (let i = 0, l = keys.length; i < l; i++) {
    if (desc.hasOwnProperty(keys[i])) {
      return true;
    }
  }

  return false;
}

export function decorate(handleDescriptor, entryArgs) {
  if (isDescriptor(entryArgs[entryArgs.length - 1])) {
    return handleDescriptor(...entryArgs, []);
  } else {
    return function () {
      return handleDescriptor(...Array.prototype.slice.call(arguments), entryArgs);
    };
  }
}

const DEFAULT_MSG = 'This function will be removed in future versions.';

function handleDescriptor(target, key, descriptor, [msg = DEFAULT_MSG, options = {url: undefined}]) {
  if (typeof descriptor.value !== 'function') {
    throw new SyntaxError('Only functions can be marked as deprecated');
  }

  const methodSignature = `${target.constructor.name}#${key}`;

  if (options.url) {
    msg += `\n\n    See ${options.url} for more details.\n\n`;
  }

  return {
    ...descriptor,
    value: function deprecationWrapper() {
      console.log(`DEPRECATION ${methodSignature}: ${msg}`);
      return descriptor.value.apply(this, arguments);
    }
  };
}

export function deprecate(...args) {
  return decorate(handleDescriptor, args);
}

https://www.reddit.com/r/Angular2/comments/7po4wq/angular_5_custom_decorators_with_aot/