CODEWITHSUNDEEP
javascriptclassscopeclosures
Shurik
Shurik

Reputation: 3

Why aren't the references to the private var's not being updated?

The add method isn't working like intended. When I have 2 time object t (all 0's), and t2 (1 minute). When I add t2 to t, t doesn't change BUT when I call my toString method on t it gives me the expected value. Here is what I mean if that makes no sense: An example of what I mean!

What I think the problem is t's global references aren't being updated after the call to add. I just can't understand why.

I would like to know why it isn't working not just how to fix the problem.

Time = function(pyear, pmonth, pdate, phour, pminute, psecond)
{
    var that = this;
    that.year = 0;
    that.month = 0;
    that.date = 0;
    that.hour = 0;
    that.minute = 0;
    that.second= 0;

    //constructor
    if(pyear !== undefined)
    {
        that.year = pyear;
        that.month = pmonth;
        that.date = pdate;
        that.hour = phour;
        that.minute = pminute;
        that.second = psecond;
    }

    //adds toAdd time object to time
    function add(toAdd)
    {
        that.year += toAdd.year;
        that.month += toAdd.month;
        that.date += toAdd.date;
        that.hour += toAdd.hour;
        that.minute += toAdd.minute;
        that.second += toAdd.second;
    }



    //returns time as a String
    function toString()
    {
        var toReturn = "";
        if(that.year < 1000)
        {
            if(that.year < 100)
            {
                if(that.year < 10)
                {
                    toReturn += "0";
                }
                toReturn += "0";
            }
            toReturn += "0";
        }

        toReturn += that.year + "-";

        if(that.month < 10)
        {
            toReturn += "0";
        }

        toReturn += that.month +"-";

        if(that.date < 10)
        {
            toReturn += "0";
        }

        toReturn += that.date +"T";

        if(that.minute < 10)
        {
            toReturn += "0";
        }

        toReturn += that.minute +":";

        if(that.second < 10)
        {
            toReturn += "0";
        }

        toReturn += that.second;
        //year +"-"+ month +"-"+ date +"T"+ hour +":"+ minute +":"+ second
        return toReturn;
    }

    return{
        year: that.year,
        month: that.month,
        date: that.date,
        hour: that.hour,
        minute: that.minute,
        second: that.second,
        add: add,
        toString: toString
    }
};

Upvotes: 0

Views: 43

Answers (2)

zmii
zmii

Reputation: 4277

Everything works. Because the function

//adds toAdd time object to time
function add(toAdd)
{
    that.year += toAdd.year;
    that.month += toAdd.month;
    that.date += toAdd.date;
    that.hour += toAdd.hour;
    that.minute += toAdd.minute;
    that.second += toAdd.second;
}

Retuns nothing, you get a undefined as a result of addition. Please try inputting t into console after adding and you will see that t is new.

Upvotes: 0

David Waters
David Waters

Reputation: 12028

When you are returning from your Time function your are returning a new object with copied values for year, month, date etc.

return{ // Create a new Object
    year: that.year,    // copy the value from that.year to year
    month: that.month,
    date: that.date,
    hour: that.hour,
    minute: that.minute,
    second: that.second,
    add: add,
    toString: toString
}

As opposed to the return statment you should just assign the function add and toString to the this reference.

 // return{
 //    year: that.year,
 //    month: that.month,
 //    date: that.date,
 //    hour: that.hour,
 //    minute: that.minute,
 //    second: that.second,
 //    add: add,
 //    toString: toString
 //}
 this.toString = toString;
 this.add = add;
}

You do not need to return a value from a constructor. See https://jsfiddle.net/dwat001/xf1Lfvv5/

Upvotes: 1

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