introduction-decorators-decorator-property-decorator-log-property-simple-getter-setter.ts

function logProperty(target: any, key: string) {
  const newKey = `_${key}`;

  Object.defineProperty(target, key, {
    get() {
      console.log(`Get: ${key} => ${this[newKey]}`);
      return this[newKey];
    },
    set(newVal) {
      console.log(`Set: ${key} => ${newVal}`);
      this[newKey] = newVal;
    },
    enumerable: true,
    configurable: true
  });
}

class Task {

  @logProperty
  public id: number;

  @logProperty
  public title: string;

  constructor(id : number, title : string) {
    this.id = id;
    this.title = title;
  }
}

const task = new Task(1, 'Write more articles');
// Set: id => 1
// Set: title => Write more articles

console.log(task.id, task.title);
// Get: id => 1
// Get: title => Write more articles
// 1 'Write more articles'