Dabbling with Transducers in JS

transducers.js

const list = [1,2,3,4,5,6,7,8,9];

const inc = x => x + 1;
const isOdd = x => x % 2 !== 0;

console.log(list.map(inc));
console.log(list.filter(isOdd))
console.log(list.map(inc).filter(isOdd))
console.log(list.reduce((acc, val) => {
  if (isOdd(inc(val))) {
    return [...acc, inc(val)];
  }
  return acc;
}, []));

const comp = (...fns) => x =>
  fns.reduceRight((prevAnswer, fn) => fn(prevAnswer), x);

const compT = (...fns) => (acc, val) => {
  const r = fns.reduceRight((prevAnswer, fn) => {
    return prevAnswer.reduce((a,v) => {
      return fn(a, v);
    }, []);  
  }, [val]);
  if (!r) {
    return acc;
  }
  if (Array.isArray(r)) {
    return [...acc, ...r];
  } 
  return [...acc, r];
};

const compMapFilter = comp(isOdd, inc);

const cmpRes = list.reduce((acc, val) => {
  const res = compMapFilter(val);
  if (res) {
    return [...acc, val];
  };
  return acc;
}, []);

console.log(cmpRes)

const mapT = mappingFn => (acc, val) => {
  return [...acc, mappingFn(val)];
};
const filterT = predicate => (acc, val) => {
  if (predicate(val)) {
    return [...acc, val];
  }
  return acc;
};

const compTs = compT(filterT(isOdd), mapT(inc));

console.log(list.reduce(mapT(inc), []));
console.log(list.reduce(filterT(isOdd), []));
console.log(list.reduce(compTs, []));