React/ReactJS: Update an Array Element in Redux Reducer State

In our previous tutorial on using Redux with React/ReactJS, we have appended a couple of objects into the Redux state variable books as its elements, which is of type array.

Now what if we have to change/update that state variable at a specific index? How do we replace an array element at index i?

The official React/ReactJS documentation suggests the use of immutability helper update() to handle such data.

We make use of the package react-addons-update. Install it.

				
					npm i react-addons-update
				
			

Import the installed react-addons-update package into your reducer.js. We introduce a new action type called UPDATE_ARRAY to update a state variable of type array (which is books here) at the particular index i. Here is how it is done. The index of the element to be changed is set at [action.id].

				
				// reducer.js
				import update from "react-addons-update";
				const INITIAL_STATE = {
					books: []
				}
				export default (state = INITIAL_STATE, action={}) => {
					switch(action.type) {
						case "UPDATE_ARRAY":
							return update(state, {
								books: {
									[action.id]: {
										$set: action.content
									}
								}
							});
						default:
							return state;
					}
				};
				
			

Inside action.js, we create one more action creator called updateArray() just to update that specific array element. Note carefully that this updateArray() function has one extra field id, which is the index of the array element which is to be replaced. We create one wrapper function called updateData() around dispatch() which will be used in the React component to send out an action to the store.

				
				// action.js
				const updateArray = (content) => {
					return {
						type: "UPDATE_ARRAY",
						id: content.id,
						content: content.element
					}
				}
				const updateData = (obj) => {
					return (dispatch) => {
						dispatch(updateArray(obj));
					}
				}
				export {
					updateData
				}
				
			

Now we get to the main component. In our previous tutorial, inside componentDidMount(), the first element that was pushed to the books state variable of type array in Redux store was

				
				{
					book_id: 1,
					title: 'Dune',
					author: 'Frank Herbert',
					year: 1965
				}
				
			

Here, we will replace it with a set of different values. We first pass the updateData() function from action.js as props to the component via mapDispatchToProps. This is an element at index 0. This is how you would do it.

				
				this.props.updateData({
					id: 0,
					element: {
						book_id: 1,
						title: 'Nineteen Eighty-Four',
						author: 'George Orwell',
						year: 1949
					}
				});
				
			

Now the old data which was at index 0 got replaced by this new data

				
					{
						book_id: 1,
						title: 'Nineteen Eighty-Four',
						author: 'George Orwell',
						year: 1949
					}