HowProgrammingWorks
diff --git a/‎JavaScript/9-optimized.js‎
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+'use strict';
+
+// Projection
+
+const id = x => x;
+
+const projection = meta => src => meta.reduce(
+  (dest, [name, fn = id, field = name]) =>
+    (dest[name] = fn(src[field]), dest), {}
+);
+
+// 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 year = date => date.getFullYear();
+const diff = y => year(new Date()) - year(new Date(y + ''));
+const upper = s => s.toUpperCase();
+
+const md = [
+  ['name'],
+  ['place', upper, 'city'],
+  ['age', diff, 'born'],
+];
+
+// Usage
+
+const p1 = projection(md);
+const data = persons.map(p1);
+console.dir(data);