AUR0820

Error Message

AUR0820: Invalid spread target <target>

Where <target> represents the problematic target encountered during rendering.

Description

This error occurs during the rendering process when Aurelia tries to apply bindings defined using the spread syntax (...${expression}). It indicates that the internal instruction generated for the spread operation was associated with an unexpected or invalid target type within the compiled template structure. This is usually an internal inconsistency or an issue arising from the template compilation process.

Cause

This error typically points to an issue within the framework's rendering logic or the compiled instructions rather than a direct mistake in the template syntax itself (though incorrect syntax could potentially lead to malformed instructions). Potential underlying causes might include:

1. Compilation Error: An error during the template compilation phase might have generated incorrect instructions for the spread operation, associating it with an inappropriate internal target representation.

2. Manual Instruction Manipulation: If compiled template instructions were manually modified or generated, the spread instruction might have been incorrectly constructed or targeted.

3. Framework Bug: There might be an edge case or bug in Aurelia's rendering engine related to handling spread syntax in specific scenarios.

Solution

Because this error often stems from internal inconsistencies, resolving it might require investigation beyond simple template syntax checks:

1. Simplify the Template: Try simplifying the template around the element using the spread syntax. Remove surrounding elements, bindings, or structural attributes (if.bind, repeat.for) temporarily to see if the error persists. This can help isolate the conflicting structure.

2. Check the Spread Expression: Ensure the object being spread (...${expression}) evaluates correctly and doesn't contain unexpected values or structures that might confuse the binding process.

3. Validate Template Syntax: Double-check the template syntax around the spread usage for any subtle errors, although basic syntax errors usually result in different error messages.

4. Update Aurelia: Ensure you are using the latest compatible version of Aurelia packages, as the issue might have been fixed in a newer release.

5. Report Issue: If the error persists after checking the above points and seems unrelated to your specific code, consider reporting it as a potential bug to the Aurelia development team, providing a minimal reproduction case if possible.

Example

It's difficult to provide a direct "incorrect" vs "correct" template example that reliably triggers this specific internal error. The error occurs after the template syntax is parsed, during the rendering instruction processing. However, a complex scenario might increase the likelihood of hitting such an edge case:

<template>
  <require from="./my-complex-component"></require>

  <!-- A complex setup where spread might potentially encounter issues -->
  <div repeat.for="item of items">
    <template if.bind="item.isActive">
      <my-complex-component ...${item.properties}></my-complex-component>
    </template>
  </div>
</template>

If AUR0820 occurs in such a scenario, the debugging steps above (simplification, checking item.properties, validating syntax, updating) should be followed.

Debugging Tips

• Identify the element using spread (...) within the template that seems related to the error.

• Use browser developer tools to inspect the elements and surrounding structure at runtime.

• Check the console for any other related errors or warnings that might provide more context.

• Try commenting out the spread binding (...${expression}) temporarily to confirm it's the source of the AUR0820 error.

• If possible, examine the compiled template instructions (this is an advanced step) to see how the spread operation is represented.