exercise 02 project euler solution.js

function* fib(a, b) {
  let c = 0
  yield a
  yield b
  while (true) {
    c = a + b
    a = b
    b = c
    yield c
  }
}

function take(n, iterable) {
  let result = [], i = 0
  while (i < n) {
    result.push(iterable.next().value)
    i++
  }
  return result
}

function takeWhile(conditionFn, iterable) {
  let result = []
  let value = take(1, iterable)
  while (conditionFn(value)) {
    result = result.concat(value)
    value = take(1, iterable)
  }
  return result
}

function sum(a,b) { return a + b }
function isEven(n) { return n % 2 === 0}

const solution = takeWhile(n => n < 4000000, fib(1,2)).filter(isEven).reduce(sum)