Pipe implementation in js

numlen.js

const len = num => {
  const isNum = !isNaN(parseFloat(num)) && isFinite(num);
  if (!isNum) {
    return new Error('not a number');
  }
  const str = num.toString().replace('.', '');

  return str.length;
}

const assertions = [
  len(4) === 1,
  len(44) === 2,
  len(444) === 3,
  len(4444) === 4,
  len(2222.11) === 6, 
  len("abc") instanceof Error, 
];

assertions.map(console.assert); 

pipe.js

// goal is to make this work
pipe(
  function a(c) {
    return c + 1;
  },
  a => a + 1,
)(3); // 5

// 1st stage, nope...
const pipe = (...args) => {
  return args.map(fn => fn())
}

// 2nd stage, not quite..
const pipe = (...args) => {
  return args.reduce((acc, fn) => {
    const ret = fn(acc);
    return ret;
  }, null);
}

// 3rd stage, it works!
const pipe = (...args) => arg => {
  return args.reduce((acc, fn) => {
    const ret = fn(acc);
    return ret;
  }, arg);
}

// 4th stage, cleanup
const pipe = (...args) => arg => {
  return args.reduce((acc, fn) => fn(acc), arg);
}