Introduction
While working with React and TypeScript, developers often encounter issues when defining state with useState. One such issue arises when trying to initialize a state variable with an array of objects. In this article, we will discuss a common mistake related to state initialization and its solution.
The Issue
Consider the following piece of code:
const [AssemblyItem, setAssemblyItem] = useState<AssemblyItem[]>([]);
When this code is added to a React component, it throws an error. The primary reasons for this error are:
Incorrect Naming Convention:
AssemblyItem (capitalized) should be reserved for TypeScript types or interfaces.
Using it as a variable name causes confusion and potential conflicts.
Proper State Initialization:
The state variable is expected to be an array of objects, and TypeScript requires clarity on what useState is handling.
The Solution
To fix this issue, follow these best practices:
1. Use Proper Naming Conventions
State variables should follow camelCase notation and be descriptive. In this case, the correct name would be assemblyItems instead of AssemblyItem to indicate that it holds multiple items.
2. Correct Type Definition in useState
The proper way to initialize the state is:
const [assemblyItems, setAssemblyItems] = useState<AssemblyItem[]>([]);
This ensures:
assemblyItems is an array of AssemblyItem objects.
The initial state is correctly set to an empty array ([]).
Applying the Fix in a Component
Here’s the corrected version of the React component that properly initializes and fetches assembly items:
import { useState, useEffect } from “react”;
const MyComponent = () => {
const [assemblyItems, setAssemblyItems] = useState<AssemblyItem[]>([]);
const [loading, setLoading] = useState<boolean>(true);
const [error, setError] = useState<string | null>(null);
useEffect(() => {
const getAssemblyItems = async () => {
try {
if (slug) {
setLoading(true);
const fetchedData = await fetchAssemblyItems(slug);
console.log(“Fetched Assembly Items:”, fetchedData);
setAssemblyItems(fetchedData);
} else {
console.warn(“Slug is undefined. Skipping fetchAssemblyItems.”);
}
} catch (error: any) {
console.error(“Error fetching assembly items:”, error);
setError(error?.message || “Failed to fetch Assembly Items.”);
} finally {
setLoading(false);
}
};
getAssemblyItems();
}, [slug]);
return (
<div>
{loading ? (
<p>Loading…</p>
) : error ? (
<p>Error: {error}</p>
) : (
<ul>
{assemblyItems.map((item) => (
<li key={item.id}>{item.name}</li>
))}
</ul>
)}
</div>
);
};
export default MyComponent;
Conclusion
Use proper naming conventions to distinguish between types and state variables.
Initialize state correctly to match the expected data structure.
Ensure TypeScript compatibility by explicitly defining the expected state type.
Following these best practices will prevent errors and ensure smoother development when using React and TypeScript together.