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Cover image for Using React useState with an object
Matt Angelosanto for LogRocket

Posted on • Originally published at blog.logrocket.com

Using React useState with an object

Written by Ochuko Onojakpor ✏️

React was created to help developers easily and efficiently perform Document Object Model (DOM) manipulations in their browsers than the conventional way using vanilla Javascript.

One of React’s most commonly used Hooks is useState, which manages states in React projects as well as objects’ states. With an object, however, we can’t update it directly or the component won’t rerender.

To solve this problem, we’ll look at how to use useState when working with objects, including the method of creating a temporary object with one property and using object destructuring to create a new object from the two existing objects.

Updating an item's state in a React object

To understand how to manage an object’s state, we must update an item’s state within the object.

In the following code sample, we’ll create a state object, shopCart, and its setter, setShopCart. shopCart then carries the object’s current state while setShopCart updates the state value of shopCart:

const [shopCart, setShopCart] = useState({});

let updatedValue = {};
updatedValue = {"item1":"juice"};
setShopCart(shopCart => ({
      ...shopCart,
      ...updatedValue
    }));
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We can then create another object, updatedValue, which carries the state value to update shopCart.

By setting the updatedValue object to the new {"item1":"juice"} value, setShopCart can update the value of the shopCart state object to the value in updatedValue.

To take a step forward, we can create a function to wrap the removed logic triggered by submitting a form:

import React, { useState } from 'react';

function App() {
 const [shopCart, setShopCart] = useState({item1:"Juice"});
 const handleChange = (e) => {
 let updatedValue = {};
 updatedValue = {item1:e.target.value};
 setShopCart(shopCart => ({
      ...shopCart,
      ...updatedValue
    }));
  }
  return (
    <div classname="App">
      <h3>useState with object in React Hooks - <a href="https://www.logrocket.com">LogRocket</a></h3>
      <br/>
      <label>Name:</label>
      <input type="text" name="item1" defaultValue={shopCart.item1} onChange={(e) => handleChange(e)}/>
      <br></br>
      <label>Output:</label>
      <pre>{JSON.stringify(shopCart, null, 2)}</pre>
    </div>
  );
}

export default App;
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By wrapping the logic we covered earlier in a handleChange function, we can handle any changes in the input field.

Within the input field, let’s set the value of the input element to the value of item1 in the shopCart object, which allows users to see its value as they make changes to it from the input field.

Next, let’s add the onChange event handler to each input element, ensuring the handleChange function triggers when we make any changes in the input field. And finally, we can display the current state of the shopCart object as we make changes to it.

Updating An Object's State In React By Adding Words To Name Field

Removing an item from an object in React

The same technique can be used to remove an item from an object:

const [shopCart, setShopCart] = useState({item1:"Juice", item2: "Icrecream"});

let copyOfObject = { ...shopCart }
delete copyOfObject['propertyToRemove']

setShopCart( shopCart => ({
      ...copyOfObject
    }));
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By creating a copy of the shopCart state object, we can delete an item from its copy, copyOfObject. We can then set the state of the original object, shopCart, to the value of the copied object, copyOfObject, using the setter object, setShopCart, which we defined earlier.

To take a step further, we can create a function to wrap the logic, which then triggers by clicking a button:

import React, { useState } from 'react';

function App() {

  const [shopCart, setShopCart] = useState({item1:"Juice", item2:"Icrecream"});

const handleClick = (item_id,e) => {
  let copiedShopCart = {...shopCart};
  delete copiedShopCart[item_id];
  setShopCart( shopCart => ({
      ...copiedShopCart
    }));
  console.log(shopCart);
}

  return (
    <div classname="App">
      <h3>useState with object in React Hooks - <a href="https://www.logrocket.com">LogRocket</a></h3>
      <br/>
      1.{shopCart.item1}
      <button onClick={(e) => handleClick("item1",e)}>delete</button>
      <br/>
      <br/>
      {shopCart.item2}
      <button onClick={(e) => handleClick("item2",e)}>delete</button>
      <pre>{JSON.stringify(shopCart, null, 2)}</pre>
    </div>
  );
}

export default App;
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Again, we wrap the logic we covered earlier in the handleClick function, which handles any click events from the buttons attached to it.

This allows us to list both items in the shopCart object and create a button for each item.

By attaching the handleClick function to the buttons using the onClick event, we can pass each item’s ID in the shopCart object to the handleClick function to detect which item to delete when the function triggers.

Removing An Item From An Object By Pressing The Delete Button

Conclusion

This article taught you how to use useState with objects, and how to update and delete items in an object using useState.

I recommend checking out this article to learn more about useState. If you have any questions, don’t hesitate to contact me on Twitter at @LordChuks3.


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Top comments (2)

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chrisczopp profile image
chris-czopp

useState() isn't meant to manage non-primitive state. It works, however it can behave weirdly with objects as they are mutable. As a matter of fact, I encountered the issue in one of my side projects which led me to React's docs where I found out the preferred way (reactjs.org/docs/hooks-reference.h...) - useReducer(). Just recently I used it to handle state of a dynamic form list and it really is more reliable and maintainable. πŸ˜ƒ

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avila profile image
Ahmed Vila

Well, for a local state, I find reducer pattern blowing things out of reasonable proportions, add Redux... result: object with 3-4 props vault-guarded across 4 files and 40 functions to mutate it, smelling like 2000's OO paradigm. Those tools have their rightful place and dozen of use cases, but this ain't one.
It's a simple rule - create and change state object only within a single scope. For everything else consider it to be immutable. To mutate create a copy then change it - again within single scope.
Delete example in the article can actually be done with one copy in a single line by spread syntax to accomplish "all except", similar to array's filter:

setShopCart( ({ item2 , ...rest }) => rest);

I usually need object props themselves so change can be made only using setter to start with, while passing setter into the sub-component to control state. Atomic setter ensures that state mutation is constrained to single scope by updating the copy of an object or creating a new one:

const [{.mouseX, mouseY }, setMousePosition] = useState({});

Cheers! :)

Timeless DEV post...

Git Concepts I Wish I Knew Years Ago

The most used technology by developers is not Javascript.

It's not Python or HTML.

It hardly even gets mentioned in interviews or listed as a pre-requisite for jobs.

I'm talking about Git and version control of course.

One does not simply learn git