How to access empty object inside constructor

Question

User1406973109 posted

Good day all,

Please I need to access an empty object declared inside a class constructor and create new properties for it.

I'm getting undefined when I try to access the object inside a method. Please check my code below:

class ShoppingCart{
  constructor(){
   this.total = 0;
    var items = {}; //Trying to access this object
  }  
  
  addItem(item_name, quantity, price){
    //Object.defineProperty(this.items, item_name, {value:quantity});
    const targetMember = "item_name"; 
    this.items[targetMember.value] = quantity; //This brings undefined
    this.total += price;
  }
  
  removeItem(item_name, quantity, price){
    this.total -= price;
  }
  
  checkout(cash_paid){
    if(cash_paid < this.total)
      {
        return 'Cash paid not enough';
      }
    else
      {
        var balance = this.total - cash_paid;
        return balance;
      }
  }
  
}

Thanks

Tim

Answer 1

User753101303 posted

Hi,

What if using just what you have done already for total ie :

this.items={};

var is for local variables( as you have done already as well for the balance)

Answer 2

User839733648 posted

Hi timotech,

The constructor method is a special method for creating and initializing an object created with a class.

There can only be one special method with the name "constructor" in a class. 

When you define a class and use this keyword to set the value, the value is recognized as a public member.

In that case, you could apply the member out of the constructor.

Here is a sample.

    <script>
        class Rectangle {
            constructor() {
                this.height = 9;
                this.width = 15;
                this.items = {name:"abc",age:11}; 
            }
        }
        const rec = new Rectangle();
        console.log(rec.height);
        console.log(rec.width);
        console.log(rec.items);
    </script>

If you use var to define a member, it is recognized as a private member in the constructor. So you could not access that out of it.

    <script>
        class Rectangle {
            constructor() {
                this.height = 9;
                this.width = 15;
                var items = {name:"abc",age:11}; 
            }
        }
        const rec = new Rectangle();
        console.log(rec.height);
        console.log(rec.width);
        console.log(rec.items);
    </script>

For more, you could refer to the MDN about this: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Classes

Best Regards,

Jenifer

Answer 3

User1406973109 posted

Thanks all for your help. I don't know what came over me, that I did not realize what I need was just "this"

Thanks all.

Tim