title: How can I do in React so that once a product is added to the cart if that product has already been added before it does not repeat a new object?
body: <p>[ I need to avoid the duplication of an object that has already been added to the cart, so that once I add it again, I only add the quantity property of the previous object, which would be the same ]</p>
  <p>[CartContext.js]</p>
  <pre><code>import React, { createContext, useState } from &quot;react&quot;;
  
  export const CarritoContext = createContext();
  
  export default function CartContext({ children }) {
    const [addToCarrito, setAddToCarrito] = useState([]);
  </code></pre>
  <p>[This is the function that I cannot modify so that it complies with a certain rule of not adding duplicates of an object that has already been added to the cart, only increasing its quantity of the already added object]</p>
  <pre><code>  function addItem(item, quantity) {
      setAddToCarrito(
        addToCarrito.filter((elemento, pos) =&gt; {
          if (elemento.item.id === item.id) {
            addToCarrito[pos].quantity += quantity;
            return false;
          }
          return true;
        })
      );
  
      if (quantity === 0) {
        setAddToCarrito([...addToCarrito]);
      } else {
        setAddToCarrito([...addToCarrito, { item, quantity }]);
      }
    }
  
    function clear() {
      setAddToCarrito([]);
    }
  
    function removeItem(itemId) {
      const newItems = addToCarrito.filter((item) =&gt; item.item.id !== itemId);
      setAddToCarrito(newItems);
    }
  
    console.log(addToCarrito);
  
    return (
      &lt;&gt;
        &lt;CarritoContext.Provider
          value={{ addToCarrito, setAddToCarrito, clear, addItem, removeItem }}
        &gt;
          {children}
        &lt;/CarritoContext.Provider&gt;
      &lt;/&gt;
    );
  }
  </code></pre>
  <p>[ItemAside.js]</p>
  <pre><code>import React, { useState, useContext } from &quot;react&quot;;
  import { Link } from &quot;react-router-dom&quot;;
  import ItemCount from &quot;../ItemCount/ItemCount&quot;;
  import { CarritoContext } from &quot;../../context/CartContext&quot;;
  
  const ItemAside = ({ jackets }) =&gt; {
    const [quantityCarro, setQuantityCarro] = useState(0);
    const [branded] = useState(jackets.brand);
  
    let { addToCarrito } = useContext(CarritoContext);
    let { setAddToCarrito } = useContext(CarritoContext);
    let { clear } = useContext(CarritoContext);
    let { addItem } = useContext(CarritoContext);
    let { removeItem } = useContext(CarritoContext);
  
    const onAdd = (cantidadCarro) =&gt; {
      setQuantityCarro(cantidadCarro);
      setAddToCarrito([
        ...addToCarrito,
        { item: jackets, quantity: cantidadCarro }
      ]);
      addItem(jackets, cantidadCarro);
    };
  
    return (
      &lt;div className=&quot;container-vertical&quot;&gt;
        &lt;aside style={{ width: &quot;100%&quot; }}&gt;
          &lt;div className=&quot;container-cuadrado&quot;&gt;
            &lt;div&gt;
              &lt;h3&gt;${jackets.price}&lt;/h3&gt;
            &lt;/div&gt;
            &lt;div&gt;
              &lt;p&gt;and FREE Returns&lt;/p&gt;
            &lt;/div&gt;
            &lt;div&gt;
              &lt;p&gt;
                Delivery for &lt;strong&gt;$39.99&lt;/strong&gt;
              &lt;/p&gt;
              &lt;p&gt;
                between &lt;strong&gt;17 - 30 April&lt;/strong&gt;
              &lt;/p&gt;
            &lt;/div&gt;
            &lt;div&gt;
              &lt;small&gt;
                &lt;span className=&quot;ubicacion&quot;&gt;&lt;/span&gt; Deliver to Argentina
              &lt;/small&gt;
            &lt;/div&gt;
  
            &lt;div&gt;
              {quantityCarro ? (
                &lt;&gt;
                  &lt;Link to=&quot;/cart&quot;&gt;
                    &lt;button className=&quot;close zbutton&quot;&gt;Buy now&lt;/button&gt;
                  &lt;/Link&gt;
                  &lt;p onClick={clear}&gt;Limpiar carro &lt;/p&gt;
                  &lt;br /&gt;
                  &lt;br /&gt;
                  &lt;p onClick={() =&gt; removeItem(jackets.id)}&gt;
                    {`Quitar ${jackets.name} de el carro`}
                  &lt;/p&gt;
                &lt;/&gt;
              ) : (
                &lt;ItemCount
                  stock={jackets.stock}
                  branded={branded}
                  initial={0}
                  onAdd={onAdd}
                /&gt;
              )}
            &lt;/div&gt;
  
            &lt;div&gt;
              &lt;div className=&quot;celwidget&quot;&gt;
                &lt;div className=&quot;a-section a-spacing-small a-text-left celwidget&quot;&gt;
                  &lt;span className=&quot;a-declarative&quot;&gt;
                    &lt;span className=&quot;aok-align-center&quot;&gt;
                      &lt;img
                        alt=&quot;&quot;
                        src=&quot;https://images-na.ssl-images-amazon.com/images/G/30/x-locale/checkout/truespc/secured-ssl._CB485936936_.png&quot;
                        height=&quot;15px&quot;
                      /&gt;
                    &lt;/span&gt;
                    &lt;span className=&quot;a-letter-space&quot;&gt;&lt;/span&gt;
                    &lt;span
                      className=&quot;dataspan&quot;
                      style={{
                        cursor: &quot;pointer&quot;,
                        color: &quot;#0099C0&quot;,
                      }}
                      data-hover=&quot;We work hard to protect your security and privacy. Our payment security system encrypts your information during transmission. We don’t share your credit card details with third-party sellers, and we don’t sell your information to others.&quot;
                    &gt;
                      Secure transaction
                    &lt;/span&gt;
                  &lt;/span&gt;
                &lt;/div&gt;
              &lt;/div&gt;
            &lt;/div&gt;
            &lt;div className=&quot;info-shipping&quot;&gt;
              &lt;div&gt;
                &lt;p&gt;Shipping from&lt;/p&gt;
                &lt;p&gt;Sold by&lt;/p&gt;
              &lt;/div&gt;
              &lt;div&gt;
                &lt;p&gt;Carvel&lt;/p&gt;
                &lt;p&gt;Carvel&lt;/p&gt;
              &lt;/div&gt;
            &lt;/div&gt;
            &lt;div className=&quot;gift-container&quot;&gt;
              &lt;label className=&quot;control control--checkbox&quot;&gt;
                &lt;input type=&quot;checkbox&quot; className=&quot;checkgift&quot; /&gt;
                &lt;small className=&quot;small-gift&quot;&gt;
                   Add a gift ticket to facilitate returns
                &lt;/small&gt;
              &lt;/label&gt;
            &lt;/div&gt;
          &lt;/div&gt;
        &lt;/aside&gt;
      &lt;/div&gt;
    );
  };
  
  export default ItemAside;
  </code></pre>