TypeError：this.list.push不是ecmascript 6中的函数

Question

When calling the add function of my GroceryList class, I get an error:

TypeError: this.list.push is not a function

Why is this?

class GroceryList {

      constructor() {
        this.list = {
            value: [],
            writable: false,
            enumerable: true  
          };
      }

        add(item) {
        this.list.push(item);
      }

      getAll() {
        return this.list;
      }

      getItemIndex(value) {
        var index = this.list.length;
        while(--index > -1) {
          if(this.list[index] === value) {
            return index;
          }
        }
        return -1;
      }
    }

Answer 1

You are confusing

• A whole object

vs

• A list as an attribute of that object

The list object contains a list, but that does not mean it is a list. You should write list.value.push(x)

Answer 2

It seems you are trying to use a property descriptor . However, those descriptors only work with Object.defineProperty .

this.list = {
  value: [],
  writable: false,
  enumerable: true  
};

literally assigns an object with the properties value , writable and enumerable to this.list .

What you seem to want is:

Object.definProperty(this, 'list', {
  value: [],
  writable: false,
  enumerable: true  
});

Now this.list returns an array, but it's not possible to assign a new value to the property.