Question

Following my last thread (here), I think I’ve pin-pointed the problem.

However, I’m getting a headache trying to understand why this is occurring.

Context: I have an Object called “Schedule” within which I’m creating 52 “week” Objects. Each week has functions to return the start and end dates in a MySQL format, the JS date Object and a label. More details in previous post.

It works perfectly, apart from when I’m trying to initiate the “EndDate”.

/* --- LEAP.Schedule.week Object --- */

LEAP.Schedule.week = function(n_date, n_week){

    this.week = n_week;

    this.date = n_date;

    this.year = this.date.getFullYear();

    this.month = this.date.getMonth();

    this.month += 1;

    this.day = this.date.getDate();

    alert("BEFORE " + this.date.getDate());

    this.end_date = this.setEndDate(this.date);

    alert("AFTER " + this.date.getDate());

};

LEAP.Schedule.week.prototype.setEndDate = function(date) {

    var ret_date = date;

    ret_date.setDate(ret_date.getDate() + 6);

    return(ret_date);

}

Using the alerts either side of “this.setEndDate” being run, I can see that “this.date” is being incremented every time “setEndDate” is being run.

I don’t want that to happen: I want “this.date” to stay as the date being passed into the week Object, and I want a separate variable called “this.end_date” which is basically this.date plus six days.

I’m presuming this is a referencing issue. I found this article: http://www.snook.ca/archives/javascript/javascript_pass/ but truth be told I don’t understand it… 🙂

Could anyone enlighten me?

Answer 1

I think it’s because you’re passing “this.date” through to setEndDate each time, so when you run ret_date.setDate you are doing it to this.date. This is because “date” is an object whose reference is being passed around.

You should be able to change it as such:

var mydate = new Date(this.date);
this.end_date = setEndDate(mydate);

The mydate object will now be modified, which won’t affect your code.

Better still, you could just tell the set end date to change the this.end_date, based on this.date and you shouldn’t need to pass anything around!