every.js

var _ = {};

_.every = function(list, condition) {
  for (var i = 0; i<list.length; i++) {
    if (!condition(list[i])) {
      return false;
    }
  }
  return true;
}

very close! condition(list[i]) could evaluate to true. and the bang would make it false. so you're just making it the opposite of what it really evaluates to. so if condition(list[i]) is false, you want to return false. so it would look something like:

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