src/index.js
function filter(a, cb) {
  var n = [];
  each(a, function(v) {
    if (cb(v)) {
      n.push(v);
    }
  });
  return n;
}
function filter(a, cb) {
  var n = [];
  each(a, function(v) {
    if (cb(v)) {
      n.push(v);
    }
  });
  return n;
}
Returns those elements of `a` for which `cb(a)` returns truthy