Question

function object() {
    var F = function() {};
    F.prototype = {
        alias: {},
        hasOwnProperty: function() { return false; },
        hasProperty: function(obj, prop) {
            for (var i = 0; i < obj.length; i++) {
                if (obj[i] !== prop) return false;
                else if (obj[i] === prop) return true;
                else return undefined;
            }
        }
    };
    return new F();
}

var newObj = object();
newObj.alias.msg = "Hello";
console.log(newObj.hasProperty(newObj.alias, "Hello"));

It returns undefined for newObj.hasProperty(newObj.alias, “Hello”). Why?

Answer 1

Well, for one thing, alias is a plain object, and therefore doesn’t have a .length property that can be used for your for loop.

If you place:

console.log(i);

…in your for loop, you’ll notice that you never actually run the block.

And even if you fixed the loop, you’re still doing a return in the very first enumeration, so if the property you’re testing isn’t first in the loop, you’ll get an incorrect result.

Ultimately, you won’t be able to replicate the behavior of hasOwnProperty() with a loop, because the prototype will be included in the enumeration.