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0.1.2 • Public • Published

Macro Decorators

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Sometimes, writing code for JavaScript getters and setters can get repetitive. Macro decorators allow you to DRY up your code by creating a decorator that can duplicate a getter/setter's functionality in multiple places!

Checkout the docs to get started, or continue reading for more information.


Using NPM:

npm install macro-decorators

Using Yarn:

yarn add macro-decorators


You can import the macro decorator from macro-decorators and use it to define macros:

import macro from 'macro-decorators';
function fullNameMacro() {
  return macro({
    get() {
      return `${this.firstName} ${this.lastName}`;
    set(obj, key, value) {
      let [firstName, lastName] = value.split(' ');
      this.firstName = firstName;
      this.lastName = lastName;
class User {
  @fullNameMacro fullName;
class Admin {
  @fullNameMacro fullName;
let captainMarvel = new User();
captainMarvel.fullName = 'Carol Danvers';
console.log(captainMarvel.firstName); // 'Carol'
console.log(captainMarvel.lastName); // 'Danvers'
console.log(captainMarvel.fullName); // 'Carol Danvers'

You can also create dynamic macros which accept parameters, to make them more reusable and composable:

import macro, { filter, reads } from 'macro-decorators';
function percent(dividendName, divisorName) {
  return macro(function() {
    let divisor = this[divisorName];
    if (!divisor) {
      return null;
    return (this[dividendName] / divisor) * 100;
function formattedPercent(percentPropertyName) {
  return macro(function() {
    let value = this[percentPropertyName];
    if (!value) {
      return '--';
    value = value.toFixed(2);
    return `${value}%`;
class TestResultComponent {
  testResults = [];
  @filter('testResults', result => !result.finished)
  @filter('testResults', result => result.finished && !result.succeeded))
  @filter('testResults', result => result.finished && result.succeeded))
  @reads('testResults.length') numberOfBuilds;
  @reads('errorBuilds.length') numberOfErrorBuilds;
  @reads('failedBuilds.length') numberOfFailedBuilds;
  @reads('passedBuilds.length') numberOfPassedBuilds;
  @percent('numberOfErrorBuilds', 'numberOfBuilds') percentOfErrorBuilds;
  @percent('numberOfFailedBuilds', 'numberOfBuilds') percentOfFailedBuilds;
  @percent('numberOfPassedBuilds', 'numberOfBuilds') percentOfPassedBuilds;
  @formattedPercent('percentOfErrorBuilds') formattedPercentOfErrorBuilds;
  @formattedPercent('percentOfFailedBuilds') formattedPercentOfFailedBuilds;
  @formattedPercent('percentOfPassedBuilds') formattedPercentOfPassedBuilds;

The macro-decorators library also ships with a number of predefined macros, including the @filter and @reads decorators from the last example. Check out the API doc for more information on these macros.

Macro Paths

Built in macros that receive a key to a different property as an argument can also receive a path of keys separated by periods:

import { reads } from 'macro-decorators';
class Person {
  friends = [];
  @reads('friends.length') numFriends;

Paths can be any length, but can only consist of string based property keys separated by periods. They cannot be dynamic.


See the Contributing guide for details.


macro-decorators is built using TypeScript, and is compatible with both the TypeScript and Babel Legacy stage 1 decorators transforms. This is following the recommendation of the decorators proposal champions.

Future Upgrade Path

The decorators spec is still changing and not finalized at all, but this library intends to provide an upgrade path for the @macro decorator and all of the macros defined in it. This plan will be finalized when the decorators proposal is at least stage 3 and beginning to see wide adoption. Ideally, it will:

  1. Be partially codemoddable
  2. Not require users to rewrite too much existing code
  3. Allow users to import both the legacy decorators and the finalized decorators at the same time, in the same app, so users can convert one file at a time.

Whether or not these goals will be technically feasible will depend on the final spec and its implementation.


This project is licensed under the MIT License.




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