simple_transducer.js

// Utils
const data = [0, 1, 2, 3, 4, 5];
const reduce = (fn) => (a) => (b)  => b.reduce(fn, a);
const compose = (fns) => (a) => fns.reduceRight((acc, fn) => fn(acc), a);

// Transducer
const mapping = (transformerFn) => (combinerFn) => (acc, v) => combinerFn(acc, transformerFn(v));
const filtering = (testFn) => (combinerFn) => (acc, v) => testFn(v) ? combinerFn(acc, v) : acc;
const dropping = (totDrop) => (combinerFn) => (acc, v) => --totDrop >= 0 ? acc : combinerFn(acc, v);
const taking = (totTake) => (combinerFn) => (acc, v) => --totTake >= 0 ? combinerFn(acc, v) : acc;

// Main Function
const mulTen = (v) => v * 10;
const gtTwo = (v) => v > 2;
const concat = (acc, v) => acc.concat(v);

const output = reduce(
    compose([
        filtering(gtTwo),
        mapping(mulTen),
        taking(2),
        dropping(1),
      ])(concat)
  )([])(data);

console.log(output); // 40