[GraphQL] Apollo React Mutation Component

const ADD_ITEM = gql`
  mutation addItem($value: String!) {
    addItem(value: $value) @client
  }
`;

const client = new ApolloClient({
  clientState: {
    defaults,
    resolvers: {
      Mutation: {
        addItem: (_, { value }, { cache }) => {
          let { items } = cache.readQuery({ query: GET_ITEMS });
          items = [...items, value];
          cache.writeData({ data: { items } });
          return null;
        }
      }
    }
  }
});


const AddItem = () => {
  let input;
  return (
    <Mutation mutation={ADD_ITEM}>
      {(addItem, { loading, error, data }) => (
        <div>
          <form
            onSubmit={e => {
              e.preventDefault();
              addItem({ variables: { value: input.value } });
              input.value = "";
              input.focus();
            }}
          >
            <input ref={node => (input = node)} />
            <button type="submit">Add Item</button>
          </form>
        </div>
      )}
    </Mutation>
  );
};