gistfile1.js

Object.prototype.explode = function() {
  return 'KABOOM!';
};


var addAll = function(things, value) {
   for (var i in things) {
      things[i].push(value);
   }
   return things;
}


var things = {
   'first' : [],
   'second' : []
};

console.log(addAll(things, 1));
// Expected: { first: [ 1 ], second: [ 1 ] }
// Actual: error! function has no method 'push'

var safeAddAll = function(things, value) {
   for (var i in things) {
      if (this.hasOwnProperty(i)) {
         things[i].push(value);
      }
   }
   return things;
}

console.log(safeAddAll(things, 1));
// { first: [ 1 ], second: [ 1 ] }