3-class.js

'use strict';

const logable = fields => {
  class Logable {
    constructor(data) {
      this.values = data;
    }
    toString() {
      let result = this.constructor.name + '\t';
      for (const key in fields) {
        result += this.values[key] + '\t';
      }
      return result;
    }
  }
  for (const key in fields) {
    Object.defineProperty(Logable.prototype, key, {
      get() {
        console.log('Reading key:', key);
        return this.values[key];
      },
      set(value) {
        console.log('Writing key:', key, value);
        const def = fields[key];
        const valid = (
          typeof value === def.type &&
          def.validate(value)
        );
        if (valid) this.values[key] = value;
        else console.log('Validation failed:', key, value);
      }
    });
  }
  return Logable;
};

// Usage

const Person = logable({
  name: { type: 'string', validate: name => name.length > 0 },
  born: { type: 'number', validate: born => !(born % 1) },
});

const p1 = new Person({ name: 'Marcus Aurelius', born: 121 });
console.log(p1.toString());
p1.born = 1923;
console.log(p1.born);
p1.born = 100.5;
p1.name = 'Victor Glushkov';
console.log(p1.toString());