javascript create object with private array

Question

I am wanting to create a private array within an object. The problem is that I am copying obj.arr with arrCopy but it seems to only reference obj.arr. This is causing issues when I splice it as it is affecting obj.arr which on any further runs of the code will be shorter.

here is a codepen with an example of the code to play with.

here is the javascript of concern

var obj = {
  min: 3,
  max: 9,
  // I want the array to be private and never to change.
  arr : [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11],
  inside: function(){
    // I want this variable to copy the arrays values into a new array that can be modified with splice()
    var arrCopy = this.arr;
      console.log('obj.arr: ' + this.arr);
      console.log('arrCopy: ' + arrCopy);
    // I want to be able to splice arrCopy without affecting obj.arr so next time the function is run it gets the value of obj.arr again
    var arrSplit = arrCopy.splice(arrCopy.indexOf(this.min), (arrCopy.indexOf(this.max) - arrCopy.indexOf(this.min) + 1));
    console.log('arrSplit: ' + arrSplit);
    console.log('obj.arr: ' + this.arr);
  }
}

//to run un-comment the next line
//obj.inside();

thanks for any help,

Regards,

Andrew

possible duplicate of Is there a method to clone an array in jQuery? — Denis
– Denis, Commented Oct 5, 2013 at 7:09

Barmar · Accepted Answer · 2013-10-05 07:09:25Z

3

When you assign objects or arrays in Javascript, it just copies a reference to the original array or object, it doesn't copy the contents. To make a copy of an array, use:

var arrCopy = this.arr.slice(0);

answered Oct 5, 2013 at 7:09

Barmar

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3 Comments

synthet1c Over a year ago

Wow that was quick!!, thanks for the answer Barmar it worked perfectly!

Patrick Evans Over a year ago

as a side note to this: if you end up putting objects/other arrays into the array and call slice it will use a reference of the objects/arrays in the new array

synthet1c Over a year ago

Thanks Patrick I will try to keep that in mind for the future.

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