applyOnPrev.js

// Some generator fun!

// WORK IN PROGRESS
// Only accepts two arguments in the `cb` call for the moment
  
"use strict";
const cbOnPrev = ((reset) => Object.defineProperty(
  function* cbOnPrev (cb) {
    let a = yield;  // Replace `yield` with `function.sent` once it's a thing
    let b = yield a;

    while (true) {
      [a, b] = [b, yield cb(a, b)];
      if (b === reset) {
        a = yield;
        b = yield a;
      }
    }
  },
  "reset",
  { value: reset }
))(Symbol("reset"));


// Usage

// Kinda Fibonacci
const fibIt = cbOnPrev((n1, n2) => n1 + n2);

fibIt.next();  // Remove this step once function.sent is a thing

let fibNum = 1;  // Starting at 0 would infini-loop!

while (fibNum < 100) {
  fibNum = fibIt.next(fibNum).value;
  console.log(fibNum);
}
// Close if you want to
fibIt.return(fibNum);

// Reset with
/*
  fibIt.next(cbOnPrev.reset);
  fibIt.next();
*/