I'm facing an issue with conditional rendering in a custom component in my React application. I've been working on creating a custom component for conditional rendering that renders content only when a specific condition is met. Here's the code I have so far
import React from 'react';
function ConditionalRenderComponent({ condition, children }) {
return (
<div>
{condition && children}
</div>
);
}
export default ConditionalRenderComponent;
While using this custom component, I noticed that the content passed through the children
prop is being accessed and executed even when the condition
is false
. This behavior is different from when I directly use condition && <div></div>
without a custom component, which correctly prevents the content from being accessed when the condition is false
.
Here's how I'm using the custom component:
import React, { useState, useEffect } from 'react';
import ConditionalRenderComponent from './ConditionalRenderComponent';
function App() {
const [userData, setUserData] = useState(null);
const isLoggedIn = userData !== null;
useEffect(() => {
setTimeout(() => {
setUserData({
username: 'john_doe',
email: 'john@example.com'
});
}, 1000);
}, []);
return (
<div>
<h1>Welcome to My App</h1>
<ConditionalRenderComponent condition={isLoggedIn}>
<div>
<p>Hello, {userData.username}!</p>
<p>Your email: {userData.email}</p>
</div>
</ConditionalRenderComponent>
{!isLoggedIn && <p>Please log in to access user data.</p>}
</div>
);
}
export default App;
In the example above, the userData
is initially null
and later populated with data retrieved from the server. The isLoggedIn
condition depends on whether the userData
is populated.
However, even when the isLoggedIn
condition is false
(before the data is fetched), the content inside the ConditionalRenderComponent
still tries to access and display the userData
. This leads to the error message: "TypeError: Cannot read properties of null (reading 'username')".
Comparison with standard conditional rendering:
Below is a comparison of the behavior using the standard condition && <div></div>
approach:
// Standard conditional rendering
{isLoggedIn && (
<div>
<p>Hello, {userData.username}!</p>
<p>Your email: {userData.email}</p>
</div>
)}
As shown in the above code, using the standard approach correctly prevents accessing the userData
values when the condition is false
.
I'm not sure why this difference in behavior is occurring when using a custom component with the children
prop. I've tried debugging and searching for solutions, but I haven't been able to find a clear answer.
I'd really appreciate any insights or suggestions on why this behavior might be happening and how I can modify the custom component to achieve the expected conditional rendering behavior using the children
prop.
Thank you in advance for your help!
So I think the reason it happens is because, in the ConditionalRenderComponent
component, the children are passed to it as a property (like arguments to a function). JSX expressions are evaluated as arguments to functions.
This means that even if the condition
is false, the children
are still evaluated before being passed to the ConditionalRenderComponent
function.
You are giving a child a PlayStation
(in your left hand) and Math paper marks
(in your right hand) and saying that if he/she scores more than 90/100, he/she will get the PlayStation.
Since the child already can see the PlayStation in your left hand (passing children
as a JSX Expression), he/she already starts using without even checking for the condition.
Now if you close your fist, synonymous to passing the children
as a function, he/she can't evalute what is in the left hand before checking if the condition is true in your right hand.
We modify our custom component by using a function as a child instead of directly rendering the children
within the component. This way, you can ensure that the evaluation of the children
only happens if the condition
is true.
function ConditionalRenderComponent({ condition, children }) {
return (
<div>
{condition && children()}
</div>
);
}
<ConditionalRenderComponent condition={isLoggedIn}>
{() => (
<div>
<p>Hello, {userData.username}!</p>
<p>Your email: {userData.email}</p>
</div>
)}
</ConditionalRenderComponent>