# AUR0759

## Error Message

`AUR0759: No attribute definition found for type <TypeName>`

Where `<TypeName>` is the name of the class that was expected to be a custom attribute.

## Description

This error occurs when Aurelia attempts to retrieve the definition metadata for a custom attribute class but fails to find it. Custom attribute definitions contain essential information like the attribute's name, bindables, and other configurations, typically provided via the `@customAttribute` decorator or inferred through conventions.

## Cause

The most common causes are:

1. **Missing Decorator/Convention:** The class intended to be a custom attribute is missing the `@customAttribute` decorator, and it doesn't follow a naming convention that allows Aurelia to automatically recognize it as such (if conventions are enabled).
2. **Incorrect Registration:** The custom attribute class might be defined but not correctly registered as a dependency within the component or application scope where it's being used.
3. **Build/Bundling Issues:** Problems during the build process might prevent the decorator metadata from being correctly emitted or associated with the class.
4. **Circular Dependencies:** Complex circular dependencies involving the custom attribute class might interfere with metadata retrieval.

## Solution

1. **Apply Decorator:** Ensure the class has the `@customAttribute('attribute-name')` decorator applied, specifying the HTML attribute name.

   ```typescript
   import { customAttribute } from 'aurelia';

   @customAttribute('my-highlight')
   export class MyHighlightAttribute {
     // ... attribute logic ...
   }
   ```
2. **Use Naming Convention:** If relying on conventions, ensure the class name follows the expected pattern (e.g., `MyHighlightCustomAttribute` might conventionally map to `my-highlight`). Verify that conventions are enabled and configured correctly in your Aurelia setup.
3. **Register Dependency:** Make sure the custom attribute is registered appropriately, either globally in `main.ts` or locally in the `dependencies` array of the component/element using it.

   ```typescript
   // In main.ts for global registration
   import { MyHighlightAttribute } from './my-highlight-attribute';
   Aurelia.register(MyHighlightAttribute /* ... other registrations */)
          // ...

   // Or in a component for local registration
   import { MyHighlightAttribute } from './my-highlight-attribute';
   import { customElement } from 'aurelia';

   @customElement({
     name: 'my-component',
     template: `<div my-highlight>...</div>`,
     dependencies: [MyHighlightAttribute]
   })
   export class MyComponent { }
   ```
4. **Check Build Configuration:** Verify your build process (e.g., Webpack, Vite configuration) correctly handles decorators and TypeScript/JavaScript compilation. Ensure `emitDecoratorMetadata` and `experimentalDecorators` (or equivalent flags) are enabled in your `tsconfig.json`.
5. **Resolve Circular Dependencies:** Analyze and refactor any circular dependencies involving the attribute class.

## Debugging Tips

* Verify the `@customAttribute` decorator is present and correctly spelled on the class definition.
* Check the name provided to the decorator (or inferred by convention) matches the usage in the HTML template.
* Confirm the attribute class is imported and included in the `dependencies` array of the consuming component or registered globally.
* Inspect the compiled JavaScript output to see if the decorator metadata seems present.
* Temporarily replace the custom attribute usage with standard HTML/bindings to rule out other template issues.