I am having some trouble understanding why I am getting an error message:

TypeError: Cannot assign to read only property 'description' of object '#'

I know that the principle is that I don't want to modify state in my reducer. Instead, I want to return a new copy of the state.

Here is my reducer:

action TOGGLE_CHECKBOX:

    {

        let copyOfItems = [...state.items]; // create a new array of items



        copyOfItems.forEach(i => i.description = newDescription);



        // return a new copy of the state

        return {

            ...state,

            items: copyOfItems

        }

    }

And here is my Reducer test:

it ('Test that each item description is set', () => {

    const state = {

        items: [

            { description: d1 },

            { description: d2 }

        ]

    }



    deepFreeze(state);



    expect(MyReducer(state, { type: TOGGLE_CHECKBOX })).toEqual({

        items: [

            { description: newDescription },

            { description: newDescription }

        ]

    });

});

However, I get the above error message. If I remove the deepFreeze the test passes. This means that I am somehow modifying the original state in some way but I can't figure out why especially because I created a new array of spreaded items.

Any help would be greatly appreciated.