JS edit variable with copied class property

Question

I dont understand why JS is doing like this. I have declared a class calendar which has an js object as property this.calendar

class SweetCalendar{
    constructor(){
        this.i_weeknumber =  46;
        this.getCalendar();
        this.filterCalender();
    }
    filterCalender(){
        var a = this.calendar
        for(var i in a){
            for(var j in a[i]){
                if(a[i][j]["Weeknumber"] != String(this.i_weeknumber)){
                    delete a[i][j];
                }
            }
        this.calendar_week
        }

With the function filterCalendar i want to create a new object which is a subset of the this.calendar property. The function works as designed but this.calendar has now the same values like this.calendar_week. I dont understand why js is doing like this. I copied the object to the variable a so why is this.calender edited by the function filterCalendar?

Can you add all of your code? I'm confused by the origins of some of your data. Is `this.calendar` initialized as a value somewhere? It would be `undefined` from what you've shown — Andrew, Nov 08 '20 at 18:02
[Duplicate](https://google.com/search?q=site%3Astackoverflow.com+js+object+copy+property+changes) of [Modifying a copy of a JavaScript object is causing the original object to change](https://stackoverflow.com/q/29050004/4642212). — Sebastian Simon, Nov 08 '20 at 18:02

score 1 · Answer 1 · answered Nov 08 '20 at 17:59

1

When assigning var a = this.calendar means that you copy the object by reverence.

Check 4 ways to clone objects in JavaScript.

answered Nov 08 '20 at 17:59

strdr4605

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score 0 · Answer 2 · answered Nov 08 '20 at 18:05

Because you never created a new object, all you did was created another reference variable which is pointing towards the same object as 'this.calender'. Consider the example below:

    var a={name:"john"};
    var b=a;
    b.name="doe";
    console.log(a.name)  //this will print doe as both a and b are pointing to the same object

You need to clone the object in order to get the functionality that you are trying to achieve.

JS edit variable with copied class property

2 Answers2