Adokiye Iruene asked a question on StackOverflow regarding applying a style on a clicked component not all the sibling components.
Change style for only clicked on view not all views
The problem is that the Asokiye generated components with a list of records in a state.
When a user clicked on a component, not only clicked component had a style applied, but also sibling components.
How can we apply a style only on a clicked component from a list of components?
If you want to know the answer you can cheat 😈 by going directly to the answer.
🗞 Preface
I will use a simple webpage that displays a list of texts wrapped in a component, Child
.
When you click on an item, the page will highlight only the clicked line. by applying the following class, highlight
.
Let’s see how to apply that style per component on click.
👩💻 Relevant Codes
Child
component returns texts and applies a style depending whether it’s clicked or not (using isClicked
prop).
App.js
renders Child components.
📊 Analysis
What needs to happen is that we need to keep a track of all on/off states of each component so that we can turn the state of each component on/off.
So let’s track on/off states.
I’ve declared it as an object, instead of as an array, I will get to it later.
(I promise 🤞)
Let’s look at what happens when a user clicks on a Child component
OK, it’s kind of hard to digest it so let’s go through it line by line.
On line#4, I am getting all previously clicked states.
const clicked = { ...prevState.clicked };
using an object spread syntax.
, toggle previous state.
clicked[i] = !clicked[i];
Lastly, set the clicked
state to the updated one.
return { clicked }; // same as return { clicked: clicked };
Note that if the property name is same as the object key, you can shorten it.
Now the question is, there is no property in the first place to set to in clicked[i] = !clicked[i]
???
⚒ A bit of Hack
OK, I’ve used a bit of JavaScript weirdness to set the clicked state of currently selected item.
I won’t go into too much details as JavaScript’s truthiness gets very hairy 😠💢).
So I refer you to this article, Mastering JavaScript’s && and || logical operators by Nicolas Marcora if you want more details.
But what you need to know is that !undefined
returns true.
So what happens in clicked[i] = !clicked[i]
is that, clicked
is an empty object initially {}
.
And !clicked[i]
will be undefined
and negating it with !
operator will turn it into true
.
clicked
object will have an item with value of 1
as the key and the on/off state as the value.
Now let’s get back to the previous question, why use an object instead of an array to keep a track of clicked states?
🤔 Why use an object?
This is to save previous memory as setting an empty array by index greater than 0 results in filling rest of space with undefined
.
Suppose that we declared state = { clicked: []}
, then setting a value above first item would populate the array with undefined
as shown below.
I’ve set a value for the 4th item, clicked[3] = !clicked[3];
and the array ended up adding the !clicked[3]
value with undefined
(<3 empty slots>) for first 3 items.
You can 👀 see ☝ that the object version stores states of clicked items only.
🚀 Full Source Code
As mentioned above, you can see the working demo on CodeSandBox.
Here is the full source code (for completeness).
👋 Partying Words
The gist is that, keep a track of each component state in an object and toggle it.
The post Keeping track of on/off states of React components appeared first on Sung's Technical Blog.
Top comments (5)
Great article Kim, I just wanted to add another approach which works better in separating the concerns of managing the state and rendering the style.
Higher order components are great tool to solve this functionality. The function
AddClick
simply manages the state of one component hence avoiding the trouble of maintaining the state of all the children component in one single component. And the best part is, you can wrap any component with this HOCAddClick
and it will get theisClicked
prop, hence improving the usability of code.Here is my alteration to your original code to make HOC work.
Here is a working example of the app stackblitz.com/edit/react-o8qsku
Thank Kushan 👍,
That's a great way to abstract the click state functionality.
I love how each Child component gets to track its own clicked state (after wrapping it with
AddClick
HoC).I've also gotten a feedback on Reddit and how someone already created a library react-on-off for such a scenario.
I believe that your HoC version is handy when good-enough is just good enough.
Never forget to use prevState. 👍
HI, thanks for this approach.
I've a little problem.... I want to be able to select only one item from the list of array and return other as false. Is there any workaround to this? Thanks
HI, thanks for the article.
I've a little problem.... I want to be able to select only one item from the list of array and return other as false. Is there any workaround to this? Thanks