# AUR0101

## Error Message

`AUR0101: Ast eval error: binding behavior "<behavior_name>" could not be found. Did you forget to register it as a dependency?`

Where `<behavior_name>` is the name of the binding behavior used in the expression.

## Description

This error occurs during the evaluation of a binding expression when a referenced binding behavior (like `debounce`, `throttle`, `signal`, etc.) cannot be located in the application's dependency injection container.

## Cause

The most common reasons for this error are:

1. **Not Registered:** The binding behavior was not registered globally (e.g., using `Aurelia.register(...)`) or locally within the component that uses it. Aurelia needs to know about the behavior to apply it.
2. **Typo:** The name of the binding behavior in the template expression is misspelled (e.g., `& debouce` instead of `& debounce`).
3. **Incorrect Import/Configuration:** If the behavior comes from a plugin or package, that package might not have been configured correctly during application startup, or the specific behavior wasn't imported/registered as instructed by the package documentation.

## Solution

1. **Register the Behavior:** Ensure the binding behavior is registered.
   * **Global Registration:** If the behavior should be available throughout the application, register it during your Aurelia application setup (often in `main.ts` or `main.js`).

     ```typescript
     import { Aurelia, StandardConfiguration } from 'aurelia';
     import { MyBindingBehavior } from './my-binding-behavior'; // Example

     Aurelia
       .register(StandardConfiguration)
       .register(MyBindingBehavior) // Register here
       .app(MyApp)
       .start();
     ```
   * **Local Registration:** If the behavior is specific to a component, register it in the component's `dependencies` array.

     ```typescript
     import { customElement } from 'aurelia';
     import { MyBindingBehavior } from './my-binding-behavior'; // Example

     @customElement({
       name: 'my-component',
       template: `<input value.bind="value & myBindingBehavior">`,
       dependencies: [MyBindingBehavior] // Register here
     })
     export class MyComponent {
       value = '';
     }
     ```
   * **Built-in Behaviors:** Standard behaviors like `debounce`, `throttle`, `signal`, `updateTrigger`, etc., are typically included with `StandardConfiguration` or `DefaultComponents`. Ensure you have registered the appropriate configuration.
2. **Check Spelling:** Carefully verify the spelling of the binding behavior name in your HTML template, ensuring it matches the registered name (usually camelCase converted to kebab-case in the template, e.g., `MyBindingBehavior` becomes `my-binding-behavior`, although the original case might also work depending on registration).
3. **Verify Plugin Configuration:** If the behavior is part of a plugin, consult the plugin's documentation to ensure it was installed and configured correctly in your application's entry point.

## Example

```html
<!-- Assumes 'debounce' behavior should be available -->

<!-- Incorrect: Typo in behavior name -->
<input value.bind="searchTerm & debouce:500">

<!-- Incorrect: Assuming 'myCustomBehavior' is not registered -->
<p textcontent.bind="message & myCustomBehavior"></p>

<!-- Correct: Using a standard, registered behavior -->
<input value.bind="searchTerm & debounce:500">

<!-- Correct: Using a custom behavior registered locally or globally -->
<p textcontent.bind="message & myCustomBehavior"></p>
```

## Debugging Tips

* Double-check the registration point (global or local) for the specific binding behavior.
* Verify the exact name used for registration and compare it (case-insensitively, considering kebab-case conversion) with the name used in the template.
* Look at your `main.ts` (or equivalent startup file) to confirm that necessary configurations (like `StandardConfiguration` or plugin registrations) are present.
* If it's a custom behavior, ensure it's correctly exported and imported where it's registered.