3-cached.js

'use strict';

// Projection

const projection = (meta) => {
  const keys = Object.keys(meta);
  return (obj) => keys.reduce((hash, key) => (
    hash[key] = meta[key]
      .reduce((val, fn, i) => (i ? fn(val) : obj[fn]), null),
    hash), {});
};

// Dataset

const persons = [
  { name: 'Marcus Aurelius', city: 'Rome', born: 121 },
  { name: 'Victor Glushkov', city: 'Rostov on Don', born: 1923 },
  { name: 'Ibn Arabi', city: 'Murcia', born: 1165 },
  { name: 'Mao Zedong', city: 'Shaoshan', born: 1893 },
  { name: 'Rene Descartes', city: 'La Haye en Touraine', born: 1596 },
];

// Metadata

const md = {
  name: ['name'],
  place: ['city', (s) => '<' + s.toUpperCase() + '>'],
  age: ['born', (year) => (
    new Date().getFullYear() - new Date(year.toString()).getFullYear()
  )]
};

// Usage

const p1 = projection(md);
const data = persons.map(p1);
console.dir(data);