zipWith implementation

zip-with.js

/*
 * zipWith(...arrays, iteratee, [thisArg]) => array
 *
 * iteratee receives an element from each array as an argument
 */

function zipWith() {
  // Argument count
  var argc = arguments.length;

  // Find iteratee, thisArg, and array count
  var fn, thisArg, arrayCount;
  if (typeof arguments[argc - 1] === "function") {
    fn = arguments[argc - 1];
    thisArg = null;
    arrayCount = argc - 1;
  } else if (typeof arguments[argc - 2] === "function") {
    fn = arguments[argc - 2];
    thisArg = arguments[argc - 1];
    arrayCount = argc - 2;
  } else {
    throw new Error("Iteratee not supplied or extra arguments given after thisArg");
  }

  // Exit early if no arrays given
  if (arrayCount === 0) return [];

  // Find length of smallest array
  var accLen = arguments[0].length;
  for (var i = 1; i < arrayCount; i++) {
    accLen = Math.min(accLen, arguments[i].length);
  }

  // Exit early if there is an empty array
  if (accLen === 0) return [];

  // Create accumulator of desired size
  var acc = new Array(accLen);

  // Populate accumulator
  for (var j = 0; j < accLen; j++) {
    var values = new Array(arrayCount);
    for (var k = 0; k < arrayCount; k++) {
      values[k] = arguments[k][j];
    }
    acc[j] = fn.apply(thisArg, values);
  }

  // Return accumulator
  return acc;
}