The code will output: 1 2 3. The for...in loop iterates over the enumerable properties of an object. In this case, it iterates over the property names 'a', 'b', and 'c' of the object. For each iteration, prop holds the current property name, and obj[prop] retrieves the value associated with that property. So, obj['a'] (which is equivalent to obj.a) gives 1, obj['b'] gives 2, and obj['c'] gives 3. The for...in loop is specifically designed for this kind of object property iteration and is not recommended for arrays.