How to join on null values SQL Server?

Reference between two properties in JavaScript Class

Hatahle

I want to create a class that includes the following properties:

List Count of List

so I thought I could do:

class MyList {
    constructor() {
        this._list = [];
        this._listCount = this._list.length;
    }
 }

With the method I defined inside, I want to be able to push items into the list and I thought it would automatically increase the _listCount but it stays static. So even though the length of the _list property is 2, the _listCount stays at 0.

Here's the method I created inside my MyList class:

add(todo) {
    this._list.push(todo);
}

Can someone explain to me why it doesn't automatically increase _listCount when I call the Method on the newly created instance?