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'is defined but never used no-unused-vars', is defined but never used no-unused-vars

asked 5 months ago

199

I'm starting a small react project (beginner) and when I cut my 'App' component into many small components, such as 'header', it doesn't work. The error started to happen as soon as I cut my header. And to say that the header css doesn't load either. You can see in the element inspector that the React component is present, but it doesn't want to load the css associated with it.

1// In App.js
2
3import React from 'react';
4import header_type from './header';
5
6
7class App extends React.Component {
8    render() {
9        return (
10
11                <div className="window">
12                    <div className="window-body">
13                        <header_type/>
14                    <div className='window_inner'>
15                        <div className="column_left">
16                        </div>
17                        <div className="column_right">
18                        </div>
19                    </div>
20                    </div>
21                </div>
22
23
24        )
25    }
26}
27
28export default App;

1// In App.js
2
3import React from 'react';
4import header_type from './header';
5
6
7class App extends React.Component {
8    render() {
9        return (
10
11                <div className="window">
12                    <div className="window-body">
13                        <header_type/>
14                    <div className='window_inner'>
15                        <div className="column_left">
16                        </div>
17                        <div className="column_right">
18                        </div>
19                    </div>
20                    </div>
21                </div>
22
23
24        )
25    }
26}
27
28export default App;

1// In header.js
2
3class header_type extends React.Component {
4    render() {
5        return (
6
7            <div className="window-header" >
8            </div>
9
10
11        )
12    }
13}
14
15export default header_type;

1// In header.js
2
3class header_type extends React.Component {
4    render() {
5        return (
6
7            <div className="window-header" >
8            </div>
9
10
11        )
12    }
13}
14
15export default header_type;

1// In index.js
2
3import React from 'react';
4import ReactDOM from 'react-dom';
5import App from '../src/components/App';
6import '../src/style/window.css';
7
8 ReactDOM.render(
9
10 <App />, document.getElementById('root')
11
12);
13

1// In index.js
2
3import React from 'react';
4import ReactDOM from 'react-dom';
5import App from '../src/components/App';
6import '../src/style/window.css';
7
8 ReactDOM.render(
9
10 <App />, document.getElementById('root')
11
12);
13

reactjs

components

11 Answers

Samarth Kamble

• answered 5 months ago

It appears you're encountering two related issues in your React project: an ESLint warning about unused variables (no-unused-vars) and CSS not loading for your header component.

The primary problem lies in the naming convention for your React component and its usage.

Issue 1: `is defined but never used no-unused-vars`

While the specific variable causing this warning isn't clear from the provided output, a common reason for it in similar scenarios, or for components not rendering, is incorrect naming.

Issue 2: CSS not loading / Component not working

React components must always start with an uppercase letter (PascalCase). When you use a component in JSX, React differentiates it from a standard HTML element (like <div> or <header>) by its initial capitalization. If it starts with a lowercase letter, React treats it as a native HTML element, not your custom component.

In your code:

You defined class header_type extends React.Component.
You imported it as import header_type from './header';.
You used it as <header_type/>.

Because header_type starts with a lowercase 'h', React interprets <header_type/> as an unknown HTML element rather than your custom React component. This means your component's render method is never called, and its content (<div className="window-header">) is never injected into the DOM by React. Consequently, the CSS associated with .window-header won't find the element it's supposed to style. The component might appear in the inspector as a generic HTML tag, not a React component instance.

Solution

To fix both issues, you need to rename your header_type component to follow React's naming conventions:

Rename the component definition: In header.js, change class header_type to class HeaderType.
```
1// In header.js
2import React from 'react'; // Don't forget to import React here!
3
4class HeaderType extends React.Component {
5    render() {
6        return (
7            <div className="window-header" >
8            </div>
9        );
10    }
11}
12
13export default HeaderType;
```
```
1// In header.js
2import React from 'react'; // Don't forget to import React here!
3
4class HeaderType extends React.Component {
5    render() {
6        return (
7            <div className="window-header" >
8            </div>
9        );
10    }
11}
12
13export default HeaderType;
```

Update the import statement: In App.js, change import header_type from './header'; to import HeaderType from './header';.

1// In App.js
2import React from 'react';
3import HeaderType from './header'; // Renamed import
4
5class App extends React.Component {
6    render() {
7        return (
8            <div className="window">
9                <div className="window-body">
10                    <HeaderType/> {/* Renamed usage */}
11                <div className='window_inner'>
12                    <div className="column_left">
13                    </div>
14                    <div className="column_right">
15                    </div>
16                </div>
17                </div>
18            </div>
19        );
20    }
21}
22
23export default App;

1// In App.js
2import React from 'react';
3import HeaderType from './header'; // Renamed import
4
5class App extends React.Component {
6    render() {
7        return (
8            <div className="window">
9                <div className="window-body">
10                    <HeaderType/> {/* Renamed usage */}
11                <div className='window_inner'>
12                    <div className="column_left">
13                    </div>
14                    <div className="column_right">
15                    </div>
16                </div>
17                </div>
18            </div>
19        );
20    }
21}
22
23export default App;

After these changes, React will correctly identify and render your HeaderType component, ensuring its JSX output (the div with window-header class) is added to the DOM. This will allow your CSS (if defined in window.css for .window-header) to apply correctly. The no-unused-vars warning related to header_type should also disappear as it's now correctly recognized and used.

Additional Notes on CSS

Ensure that your ../src/style/window.css file contains a CSS rule for .window-header, for example:

1/* In src/style/window.css */
2.window-header {
3    background-color: lightblue;
4    padding: 10px;
5    /* Add other styles as needed */
6}

1/* In src/style/window.css */
2.window-header {
3    background-color: lightblue;
4    padding: 10px;
5    /* Add other styles as needed */
6}

Samarth Kamble

• answered 5 months ago

It appears you're encountering two related issues in your React project: an ESLint warning about unused variables (no-unused-vars) and CSS not loading for your header component.

The primary problem lies in the naming convention for your React component and its usage.

Issue 1: `is defined but never used no-unused-vars`

While the specific variable causing this warning isn't clear from the provided output, a common reason for it in similar scenarios, or for components not rendering, is incorrect naming.

Issue 2: CSS not loading / Component not working

In your code:

You defined class header_type extends React.Component.
You imported it as import header_type from './header';.
You used it as <header_type/>.

Solution

To fix both issues, you need to rename your header_type component to follow React's naming conventions:

Rename the component definition: In header.js, change class header_type to class HeaderType.
```
1// In header.js
2import React from 'react'; // Don't forget to import React here!
3
4class HeaderType extends React.Component {
5    render() {
6        return (
7            <div className="window-header" >
8            </div>
9        );
10    }
11}
12
13export default HeaderType;
```
```
1// In header.js
2import React from 'react'; // Don't forget to import React here!
3
4class HeaderType extends React.Component {
5    render() {
6        return (
7            <div className="window-header" >
8            </div>
9        );
10    }
11}
12
13export default HeaderType;
```

Update the import statement: In App.js, change import header_type from './header'; to import HeaderType from './header';.

1// In App.js
2import React from 'react';
3import HeaderType from './header'; // Renamed import
4
5class App extends React.Component {
6    render() {
7        return (
8            <div className="window">
9                <div className="window-body">
10                    <HeaderType/> {/* Renamed usage */}
11                <div className='window_inner'>
12                    <div className="column_left">
13                    </div>
14                    <div className="column_right">
15                    </div>
16                </div>
17                </div>
18            </div>
19        );
20    }
21}
22
23export default App;

1// In App.js
2import React from 'react';
3import HeaderType from './header'; // Renamed import
4
5class App extends React.Component {
6    render() {
7        return (
8            <div className="window">
9                <div className="window-body">
10                    <HeaderType/> {/* Renamed usage */}
11                <div className='window_inner'>
12                    <div className="column_left">
13                    </div>
14                    <div className="column_right">
15                    </div>
16                </div>
17                </div>
18            </div>
19        );
20    }
21}
22
23export default App;

Additional Notes on CSS

Ensure that your ../src/style/window.css file contains a CSS rule for .window-header, for example:

1/* In src/style/window.css */
2.window-header {
3    background-color: lightblue;
4    padding: 10px;
5    /* Add other styles as needed */
6}

1/* In src/style/window.css */
2.window-header {
3    background-color: lightblue;
4    padding: 10px;
5    /* Add other styles as needed */
6}

Samarth Kamble

• answered 5 months ago

It appears you're encountering two related issues in your React project: an ESLint warning about unused variables (no-unused-vars) and CSS not loading for your header component.

The primary problem lies in the naming convention for your React component and its usage.

Issue 1: `is defined but never used no-unused-vars`

While the specific variable causing this warning isn't clear from the provided output, a common reason for it in similar scenarios, or for components not rendering, is incorrect naming.

Issue 2: CSS not loading / Component not working

In your code:

You defined class header_type extends React.Component.
You imported it as import header_type from './header';.
You used it as <header_type/>.

Solution

To fix both issues, you need to rename your header_type component to follow React's naming conventions:

Rename the component definition: In header.js, change class header_type to class HeaderType.
```
1// In header.js
2import React from 'react'; // Don't forget to import React here!
3
4class HeaderType extends React.Component {
5    render() {
6        return (
7            <div className="window-header" >
8            </div>
9        );
10    }
11}
12
13export default HeaderType;
```
```
1// In header.js
2import React from 'react'; // Don't forget to import React here!
3
4class HeaderType extends React.Component {
5    render() {
6        return (
7            <div className="window-header" >
8            </div>
9        );
10    }
11}
12
13export default HeaderType;
```

Update the import statement: In App.js, change import header_type from './header'; to import HeaderType from './header';.

1// In App.js
2import React from 'react';
3import HeaderType from './header'; // Renamed import
4
5class App extends React.Component {
6    render() {
7        return (
8            <div className="window">
9                <div className="window-body">
10                    <HeaderType/> {/* Renamed usage */}
11                <div className='window_inner'>
12                    <div className="column_left">
13                    </div>
14                    <div className="column_right">
15                    </div>
16                </div>
17                </div>
18            </div>
19        );
20    }
21}
22
23export default App;

1// In App.js
2import React from 'react';
3import HeaderType from './header'; // Renamed import
4
5class App extends React.Component {
6    render() {
7        return (
8            <div className="window">
9                <div className="window-body">
10                    <HeaderType/> {/* Renamed usage */}
11                <div className='window_inner'>
12                    <div className="column_left">
13                    </div>
14                    <div className="column_right">
15                    </div>
16                </div>
17                </div>
18            </div>
19        );
20    }
21}
22
23export default App;

Additional Notes on CSS

Ensure that your ../src/style/window.css file contains a CSS rule for .window-header, for example:

1/* In src/style/window.css */
2.window-header {
3    background-color: lightblue;
4    padding: 10px;
5    /* Add other styles as needed */
6}

1/* In src/style/window.css */
2.window-header {
3    background-color: lightblue;
4    padding: 10px;
5    /* Add other styles as needed */
6}

Samarth Kamble

• answered 5 months ago

It appears you're encountering two related issues in your React project: an ESLint warning about unused variables (no-unused-vars) and CSS not loading for your header component.

The primary problem lies in the naming convention for your React component and its usage.

Issue 1: `is defined but never used no-unused-vars`

While the specific variable causing this warning isn't clear from the provided output, a common reason for it in similar scenarios, or for components not rendering, is incorrect naming.

Issue 2: CSS not loading / Component not working

In your code:

You defined class header_type extends React.Component.
You imported it as import header_type from './header';.
You used it as <header_type/>.

Solution

To fix both issues, you need to rename your header_type component to follow React's naming conventions:

Rename the component definition: In header.js, change class header_type to class HeaderType.
```
1// In header.js
2import React from 'react'; // Don't forget to import React here!
3
4class HeaderType extends React.Component {
5    render() {
6        return (
7            <div className="window-header" >
8            </div>
9        );
10    }
11}
12
13export default HeaderType;
```
```
1// In header.js
2import React from 'react'; // Don't forget to import React here!
3
4class HeaderType extends React.Component {
5    render() {
6        return (
7            <div className="window-header" >
8            </div>
9        );
10    }
11}
12
13export default HeaderType;
```

Update the import statement: In App.js, change import header_type from './header'; to import HeaderType from './header';.

1// In App.js
2import React from 'react';
3import HeaderType from './header'; // Renamed import
4
5class App extends React.Component {
6    render() {
7        return (
8            <div className="window">
9                <div className="window-body">
10                    <HeaderType/> {/* Renamed usage */}
11                <div className='window_inner'>
12                    <div className="column_left">
13                    </div>
14                    <div className="column_right">
15                    </div>
16                </div>
17                </div>
18            </div>
19        );
20    }
21}
22
23export default App;

1// In App.js
2import React from 'react';
3import HeaderType from './header'; // Renamed import
4
5class App extends React.Component {
6    render() {
7        return (
8            <div className="window">
9                <div className="window-body">
10                    <HeaderType/> {/* Renamed usage */}
11                <div className='window_inner'>
12                    <div className="column_left">
13                    </div>
14                    <div className="column_right">
15                    </div>
16                </div>
17                </div>
18            </div>
19        );
20    }
21}
22
23export default App;

Additional Notes on CSS

Ensure that your ../src/style/window.css file contains a CSS rule for .window-header, for example:

1/* In src/style/window.css */
2.window-header {
3    background-color: lightblue;
4    padding: 10px;
5    /* Add other styles as needed */
6}

1/* In src/style/window.css */
2.window-header {
3    background-color: lightblue;
4    padding: 10px;
5    /* Add other styles as needed */
6}

Samarth Kamble

• answered 5 months ago

It appears you're encountering two related issues in your React project: an ESLint warning about unused variables (no-unused-vars) and CSS not loading for your header component.

The primary problem lies in the naming convention for your React component and its usage.

Issue 1: `is defined but never used no-unused-vars`

While the specific variable causing this warning isn't clear from the provided output, a common reason for it in similar scenarios, or for components not rendering, is incorrect naming.

Issue 2: CSS not loading / Component not working

In your code:

You defined class header_type extends React.Component.
You imported it as import header_type from './header';.
You used it as <header_type/>.

Solution

To fix both issues, you need to rename your header_type component to follow React's naming conventions:

Rename the component definition: In header.js, change class header_type to class HeaderType.
```
1// In header.js
2import React from 'react'; // Don't forget to import React here!
3
4class HeaderType extends React.Component {
5    render() {
6        return (
7            <div className="window-header" >
8            </div>
9        );
10    }
11}
12
13export default HeaderType;
```
```
1// In header.js
2import React from 'react'; // Don't forget to import React here!
3
4class HeaderType extends React.Component {
5    render() {
6        return (
7            <div className="window-header" >
8            </div>
9        );
10    }
11}
12
13export default HeaderType;
```

Update the import statement: In App.js, change import header_type from './header'; to import HeaderType from './header';.

1// In App.js
2import React from 'react';
3import HeaderType from './header'; // Renamed import
4
5class App extends React.Component {
6    render() {
7        return (
8            <div className="window">
9                <div className="window-body">
10                    <HeaderType/> {/* Renamed usage */}
11                <div className='window_inner'>
12                    <div className="column_left">
13                    </div>
14                    <div className="column_right">
15                    </div>
16                </div>
17                </div>
18            </div>
19        );
20    }
21}
22
23export default App;

1// In App.js
2import React from 'react';
3import HeaderType from './header'; // Renamed import
4
5class App extends React.Component {
6    render() {
7        return (
8            <div className="window">
9                <div className="window-body">
10                    <HeaderType/> {/* Renamed usage */}
11                <div className='window_inner'>
12                    <div className="column_left">
13                    </div>
14                    <div className="column_right">
15                    </div>
16                </div>
17                </div>
18            </div>
19        );
20    }
21}
22
23export default App;

Additional Notes on CSS

Ensure that your ../src/style/window.css file contains a CSS rule for .window-header, for example:

1/* In src/style/window.css */
2.window-header {
3    background-color: lightblue;
4    padding: 10px;
5    /* Add other styles as needed */
6}

1/* In src/style/window.css */
2.window-header {
3    background-color: lightblue;
4    padding: 10px;
5    /* Add other styles as needed */
6}

Samarth Kamble

• answered 5 months ago

It appears you're encountering two related issues in your React project: an ESLint warning about unused variables (no-unused-vars) and CSS not loading for your header component.

The primary problem lies in the naming convention for your React component and its usage.

Issue 1: `is defined but never used no-unused-vars`

While the specific variable causing this warning isn't clear from the provided output, a common reason for it in similar scenarios, or for components not rendering, is incorrect naming.

Issue 2: CSS not loading / Component not working

In your code:

You defined class header_type extends React.Component.
You imported it as import header_type from './header';.
You used it as <header_type/>.

Solution

To fix both issues, you need to rename your header_type component to follow React's naming conventions:

Rename the component definition: In header.js, change class header_type to class HeaderType.
```
1// In header.js
2import React from 'react'; // Don't forget to import React here!
3
4class HeaderType extends React.Component {
5    render() {
6        return (
7            <div className="window-header" >
8            </div>
9        );
10    }
11}
12
13export default HeaderType;
```
```
1// In header.js
2import React from 'react'; // Don't forget to import React here!
3
4class HeaderType extends React.Component {
5    render() {
6        return (
7            <div className="window-header" >
8            </div>
9        );
10    }
11}
12
13export default HeaderType;
```

Update the import statement: In App.js, change import header_type from './header'; to import HeaderType from './header';.

1// In App.js
2import React from 'react';
3import HeaderType from './header'; // Renamed import
4
5class App extends React.Component {
6    render() {
7        return (
8            <div className="window">
9                <div className="window-body">
10                    <HeaderType/> {/* Renamed usage */}
11                <div className='window_inner'>
12                    <div className="column_left">
13                    </div>
14                    <div className="column_right">
15                    </div>
16                </div>
17                </div>
18            </div>
19        );
20    }
21}
22
23export default App;

1// In App.js
2import React from 'react';
3import HeaderType from './header'; // Renamed import
4
5class App extends React.Component {
6    render() {
7        return (
8            <div className="window">
9                <div className="window-body">
10                    <HeaderType/> {/* Renamed usage */}
11                <div className='window_inner'>
12                    <div className="column_left">
13                    </div>
14                    <div className="column_right">
15                    </div>
16                </div>
17                </div>
18            </div>
19        );
20    }
21}
22
23export default App;

Additional Notes on CSS

Ensure that your ../src/style/window.css file contains a CSS rule for .window-header, for example:

1/* In src/style/window.css */
2.window-header {
3    background-color: lightblue;
4    padding: 10px;
5    /* Add other styles as needed */
6}

1/* In src/style/window.css */
2.window-header {
3    background-color: lightblue;
4    padding: 10px;
5    /* Add other styles as needed */
6}

Samarth Kamble

• answered 5 months ago

It appears you're encountering two related issues in your React project: an ESLint warning about unused variables (no-unused-vars) and CSS not loading for your header component.

The primary problem lies in the naming convention for your React component and its usage.

Issue 1: `is defined but never used no-unused-vars`

While the specific variable causing this warning isn't clear from the provided output, a common reason for it in similar scenarios, or for components not rendering, is incorrect naming.

Issue 2: CSS not loading / Component not working

In your code:

You defined class header_type extends React.Component.
You imported it as import header_type from './header';.
You used it as <header_type/>.

Solution

To fix both issues, you need to rename your header_type component to follow React's naming conventions:

Rename the component definition: In header.js, change class header_type to class HeaderType.
```
1// In header.js
2import React from 'react'; // Don't forget to import React here!
3
4class HeaderType extends React.Component {
5    render() {
6        return (
7            <div className="window-header" >
8            </div>
9        );
10    }
11}
12
13export default HeaderType;
```
```
1// In header.js
2import React from 'react'; // Don't forget to import React here!
3
4class HeaderType extends React.Component {
5    render() {
6        return (
7            <div className="window-header" >
8            </div>
9        );
10    }
11}
12
13export default HeaderType;
```

Update the import statement: In App.js, change import header_type from './header'; to import HeaderType from './header';.

1// In App.js
2import React from 'react';
3import HeaderType from './header'; // Renamed import
4
5class App extends React.Component {
6    render() {
7        return (
8            <div className="window">
9                <div className="window-body">
10                    <HeaderType/> {/* Renamed usage */}
11                <div className='window_inner'>
12                    <div className="column_left">
13                    </div>
14                    <div className="column_right">
15                    </div>
16                </div>
17                </div>
18            </div>
19        );
20    }
21}
22
23export default App;

1// In App.js
2import React from 'react';
3import HeaderType from './header'; // Renamed import
4
5class App extends React.Component {
6    render() {
7        return (
8            <div className="window">
9                <div className="window-body">
10                    <HeaderType/> {/* Renamed usage */}
11                <div className='window_inner'>
12                    <div className="column_left">
13                    </div>
14                    <div className="column_right">
15                    </div>
16                </div>
17                </div>
18            </div>
19        );
20    }
21}
22
23export default App;

Additional Notes on CSS

Ensure that your ../src/style/window.css file contains a CSS rule for .window-header, for example:

1/* In src/style/window.css */
2.window-header {
3    background-color: lightblue;
4    padding: 10px;
5    /* Add other styles as needed */
6}

1/* In src/style/window.css */
2.window-header {
3    background-color: lightblue;
4    padding: 10px;
5    /* Add other styles as needed */
6}

Samarth Kamble

• answered 5 months ago

The ESLint warning "'is defined but never used no-unused-vars'" in the context of React usually indicates a conflict with React's component naming conventions, especially when combined with issues like components not rendering or CSS not loading.

Here's a breakdown of the problem and the solution:

1. React Component Naming Convention (Primary Issue)

React components must start with an uppercase letter (PascalCase). When you use a lowercase name like header_type in JSX, React treats it as a standard HTML element (like div or span), not your custom component.

Impact on no-unused-vars: Since <header_type/> is interpreted as an HTML tag, the imported header_type from ./header is never actually used as a React component. This leads to the ESLint warning.
Impact on Rendering: The component effectively doesn't render as you intend, causing the "it doesn't work" issue.

2. CSS Loading Issue

For component-specific CSS, the CSS file should be imported directly into the component file that uses those styles. Your index.js imports window.css, which is fine for global styles, but header.css (or any CSS specifically for window-header) needs to be imported in header.js.

Corrected Code

To resolve both the ESLint warning and the rendering/CSS issues, follow these steps:

`App.js`

1import React from 'react';
2import Header from './header'; // Changed import name to PascalCase
3
4class App extends React.Component {
5    render() {
6        return (
7            <div className="window">
8                <div className="window-body">
9                    <Header/> {/* Changed usage to PascalCase */}
10                    <div className='window_inner'>
11                        <div className="column_left">
12                        </div>
13                        <div className="column_right">
14                        </div>
15                    </div>
16                </div>
17            </div>
18        )
19    }
20}
21
22export default App;

1import React from 'react';
2import Header from './header'; // Changed import name to PascalCase
3
4class App extends React.Component {
5    render() {
6        return (
7            <div className="window">
8                <div className="window-body">
9                    <Header/> {/* Changed usage to PascalCase */}
10                    <div className='window_inner'>
11                        <div className="column_left">
12                        </div>
13                        <div className="column_right">
14                        </div>
15                    </div>
16                </div>
17            </div>
18        )
19    }
20}
21
22export default App;

`header.js`

1import React from 'react'; // Essential for JSX files
2import './header.css'; // Import component-specific CSS (create this file if it doesn't exist)
3
4class Header extends React.Component { // Changed component name to PascalCase
5    render() {
6        return (
7            <div className="window-header" >
8            </div>
9        )
10    }
11}
12
13export default Header; // Changed export name to PascalCase

1import React from 'react'; // Essential for JSX files
2import './header.css'; // Import component-specific CSS (create this file if it doesn't exist)
3
4class Header extends React.Component { // Changed component name to PascalCase
5    render() {
6        return (
7            <div className="window-header" >
8            </div>
9        )
10    }
11}
12
13export default Header; // Changed export name to PascalCase

`index.js` (No changes needed, but ensure it looks like this)

1import React from 'react';
2import ReactDOM from 'react-dom';
3import App from '../src/components/App'; // Adjust path if necessary
4import '../src/style/window.css'; // Global styles
5
6ReactDOM.render(
7    <App />, 
8    document.getElementById('root')
9);

1import React from 'react';
2import ReactDOM from 'react-dom';
3import App from '../src/components/App'; // Adjust path if necessary
4import '../src/style/window.css'; // Global styles
5
6ReactDOM.render(
7    <App />, 
8    document.getElementById('root')
9);

Summary of Changes and Why:

Component Naming: Renamed header_type to Header in both header.js (definition and export) and App.js (import and usage). This adheres to React's component naming convention.
import React from 'react';: Added this import to header.js. While not always strictly necessary in newer React versions with certain Babel configurations (JSX transform), it's good practice and prevents issues, especially in class components.
CSS Import: Added import './header.css'; to header.js. This ensures that any styles defined in header.css (e.g., for the .window-header class) are loaded specifically for your Header component. Make sure you have a header.css file in the same directory as header.js with your styles.

Samarth Kamble

• answered 5 months ago

The warning is defined but never used no-unused-vars indicates that a variable, function, or function parameter has been declared in the code but is not being actively utilized within the same scope. This warning is typically generated by a linter, such as ESLint, which is a tool used to identify and report problematic patterns found in JavaScript code.

In your specific React project, this warning for header_type in App.js and the CSS not loading are both stemming from a common issue: React component naming conventions.

Explanation of the Issue

React components must start with an uppercase letter. When you import header_type and then try to use <header_type/> in your JSX, React (and subsequently your build tools) treats header_type as a standard HTML tag or a custom element that isn't a React component, because its name begins with a lowercase letter.

no-unused-vars Warning: Since header_type is not recognized as a React component, it's not being "used" in the way React expects. Therefore, the linter correctly identifies that the import header_type from './header'; statement is bringing in something that isn't being utilized as a functional React component, leading to the no-unused-vars warning.
CSS Not Loading: Because <header_type/> is not correctly rendered as your header.js component, its structure and class names (like window-header) are likely not being correctly inserted into the DOM by React. If the DOM element with className="window-header" isn't present, the CSS rules targeting it won't apply.

Solution

Rename your component files and the component names themselves to start with an uppercase letter.

1. Rename header.js to Header.js (Optional but good practice for consistency).

2. Modify header.js (or Header.js):

1// In Header.js
2import React from 'react';
3
4class Header extends React.Component { // Change header_type to Header
5    render() {
6        return (
7            <div className="window-header">
8            </div>
9        );
10    }
11}
12
13export default Header; // Change header_type to Header

1// In Header.js
2import React from 'react';
3
4class Header extends React.Component { // Change header_type to Header
5    render() {
6        return (
7            <div className="window-header">
8            </div>
9        );
10    }
11}
12
13export default Header; // Change header_type to Header

3. Modify App.js:

1// In App.js
2import React from 'react';
3import Header from './Header'; // Change header_type to Header and './header' to './Header'
4
5class App extends React.Component {
6    render() {
7        return (
8            <div className="window">
9                <div className="window-body">
10                    <Header /> {/* Change <header_type/> to <Header/> */}
11                    <div className='window_inner'>
12                        <div className="column_left">
13                        </div>
14                        <div className="column_right">
15                        </div>
16                    </div>
17                </div>
18            </div>
19        );
20    }
21}
22
23export default App;

1// In App.js
2import React from 'react';
3import Header from './Header'; // Change header_type to Header and './header' to './Header'
4
5class App extends React.Component {
6    render() {
7        return (
8            <div className="window">
9                <div className="window-body">
10                    <Header /> {/* Change <header_type/> to <Header/> */}
11                    <div className='window_inner'>
12                        <div className="column_left">
13                        </div>
14                        <div className="column_right">
15                        </div>
16                    </div>
17                </div>
18            </div>
19        );
20    }
21}
22
23export default App;

By following the React component naming convention, your Header component will be correctly recognized, rendered, and the associated CSS will apply as expected.

Samarth Kamble

• answered 5 months ago

The warning "'variableName' is defined but never used no-unused-vars" indicates that a variable, function, or function parameter has been declared in the code but is not being actively utilized within the same scope. This warning is typically generated by a linter, such as ESLint, which is a tool used to identify and report problematic patterns found in JavaScript code.