find.js

var _ = {};

_.find = function(list, condition) {
  var resultArray = [];
  for (var i = 0; i<list.length; i++) {
    if (condition(list[i])) {
      resultArray.push(list[i]);
    }
  }
  if (resultArray.length) {
    return resultArray[0];
  }
  return undefined;
}

so i think is more complicated than it needs to be. if a value passes the truth test, return out immediately... if there isn't one that passes the truth test in that list, then you return undefined...so think about the first part of how _.find works, specifically "return out immediately" if you find a value that passes the truth test. you could simply write it like this then:

_.find = function(list, condition) {
  for (var i = 0; i<list.length; i++) {
    if (condition(list[i])) {
      return list[i];
    }
  }
  return undefined;
}