How can I check whether an item exists in localstorage or not using pure javascript

Question

I have a project on pure javascript,and I was working on saving items to localstorage. I only need to save id , name and image of the item i am saving.

My major problem , however is i do not want save duplicate .Therefore before i save i must check whether the exists or not.

I have so far tried several approaches but all seems not to work.Below is my code snippets.

I am able to save item to localstorage with no problems, infact i can save and delete items from localstorage correctly.

const cart_DB = new cartDB();

if( cart_DB.isAddedToCart(cartInfo.id) === false) {

    // save item to database

}else {
    alert('item already in cart');
    return false;
}

class cartDB {



            /// save cart into localstorage ////
            saveIntoDB(cart) {
                const carts = this.getFromDB();

                carts.push(cart);

                // add the new array into localstorage
                localStorage.setItem('carts', JSON.stringify(carts));
            }
            /// save cart into localstorage ///



            /// return carts from storage ///
            getFromDB() {
                let carts;

                // check from local storage
                if (localStorage.getItem('carts') === null) {
                    carts = [];
                } else {
                    carts = JSON.parse(localStorage.getItem('carts'))
                }

                return carts;

            }
            /// carts from storage ends ///

        /// check if item already exists in database //////// 
    isAddedToCart(id) {

    if (localStorage.getItem(id) === null 
            ||localStorage.getItem(id).length === 0) {
                      return false;
                        }else {

                      return true;
                        }
            }
      //// checking items ends here ///////

}

What i want is to check whether the item exists or not before adding another item.

Answer 1

Assuming that you store items in array you can use below function to check if item already exists:

function checkIfItemExists (id) {
  const items = localStorage.getItem('carts') 
  let itemExists = false
  if (items) {
    const itemsData = JSON.parse(items)
    // check if item with given id exists in local storage data
    itemExists =  itemsData.find(item => item.id === id)
  }

  return itemExists
}

Answer 2

If your goal is to find out if there's a duplicate, Array.some() would be the best function you are looking for. Implement it to your function like this.

isAddedToCart(id) {
    const carts = localStorage.getItem('carts');
    return carts.some(cart => cart.id == id);
}

Array.some() Definition and Usage

The some() method checks if any of the elements in an array pass a test (provided as a function).

The some() method executes the function once for each element present in the array:

• If it finds an array element where the function returns a true value, some() returns true (and does not check the remaining values)

• Otherwise it returns false