AUR9999

Error Message

AUR9999: No scope context for spread binding.

Description

This error occurs when Aurelia attempts to bind or update a spread attribute binding (e.g., <my-component ...userSettings>), but it cannot find the necessary scope (binding context) required to evaluate the expression being spread (userSettings in the example).

Spread bindings work by evaluating an expression that should result in an object. The properties of this object are then applied ("spread") onto the target element, typically matching bindable properties of a custom element or attribute. This evaluation process requires a valid scope.

Cause

This is an internal error and should generally not happen in standard application code. Potential (though unlikely) causes could involve:

1. Manual DOM Manipulation: Modifying the DOM structure in a way that detaches the element with the spread binding from its expected parent or Aurelia-controlled hierarchy, losing the scope context.

2. Internal Errors: An unexpected state within Aurelia's rendering or binding engine, possibly due to interactions with complex custom elements, template controllers, or advanced composition scenarios.

3. Incorrect Manual Instantiation: Manually creating or manipulating SpreadBinding instances without providing the correct scope context during the binding lifecycle.

Solution

As this is typically an internal error, the solutions focus on ensuring standard usage patterns:

1. Avoid Complex DOM Manipulation: Refrain from manually manipulating the DOM within Aurelia's rendering boundaries, especially around elements using spread syntax. Let Aurelia manage the DOM structure.

2. Simplify Template Structure: If the error occurs in a complex template, try simplifying the structure involving the spread binding to isolate the issue. Check interactions with surrounding custom elements, template controllers (if.bind, repeat.for), or composition elements (au-compose).

3. Review Component Lifecycle: Ensure that any data required for the spread object is available when the binding occurs.

4. Report the Issue: If you encounter this error under normal usage conditions and cannot resolve it by simplifying the template, it might indicate an underlying issue in the framework. Consider reporting it to the Aurelia team with a reproducible example.

Example

Spread syntax itself is valid:

<!-- Standard usage (should not cause AUR9999) -->
<template>
  <user-profile ...profileData></user-profile>
</template>

// View Model
import { customElement } from 'aurelia';
import './user-profile'; // Assume user-profile element is registered

@customElement({ /* ... */ })
export class MyApp {
  profileData = {
    name: 'John Doe',
    email: '[email protected]',
    isAdmin: false
  };
}

This error would occur if, during the binding of ...profileData, the SpreadBinding instance somehow lost its connection to the scope containing profileData.

Debugging Tips

• This error is hard to debug from application code as it signals an issue within the binding mechanism's context handling.

• Use browser developer tools to inspect the element with the spread binding and its ancestors. Check if it's correctly positioned within the Aurelia component hierarchy.

• Look for any $scope or context-related properties on the element or its controllers in the debugger – they might be unexpectedly null or undefined.

• Simplify the component's template dramatically to see if the error persists, gradually reintroducing parts to pinpoint the trigger.

• Consider commenting out the spread binding (<!-- <my-component ...spreadData> -->) to confirm it's the source of the error.