Question

Why does the following returns undefined?

var global_vars = 
{

    countNumOfProperties : 
        function (obj) 
        {
            var count = 0;
            for (var k in obj) {
                if (obj.hasOwnProperty(k)) {
                    ++count;
                }
                return count;
            }
        }    
};


var DS =
{
    file_types_lookup : {}
};


global_vars.countNumOfProperties(DS.file_types_lookup)

Answer 1

The return statement is inside the loop so is never reached.

        for (var k in obj) {
            if (obj.hasOwnProperty(k)) {
                ++count;
            }
            return count;
        }

should probably be

        for (var k in obj) {
            if (obj.hasOwnProperty(k)) {
                ++count;
            }
        }
        return count;

That way, each property will be checked before the sum is returned.

As written, the function will return

• 1 to indicate that the first enumerable property is an own property, or
• 0 to indicate that there are no own properties but there are enumerable inherited properties, or
• undefined to indicate that there are no enumerable properties own or otherwise.