> For the complete documentation index, see [llms.txt](https://docs.aurelia.io/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.aurelia.io/developer-guides/error-messages/runtime-html/aur0102.md).

# AUR0102

## Error Message

`AUR0102: Ast eval error: binding behavior "<behavior_name>" already applied.`

Where `<behavior_name>` is the name of the binding behavior applied multiple times.

## Description

This error occurs when the same binding behavior (e.g., `debounce`, `throttle`) is applied more than once to a single binding expression in the template. Each behavior should only be applied once per expression.

## Cause

The most common causes are:

1. **Accidental Repetition:** Simply typing the same binding behavior twice in the expression (e.g., `value & debounce & debounce`).
2. **Redundant Behaviors:** Applying two different binding behaviors that serve mutually exclusive purposes on the same binding (e.g., applying both `throttle` and `debounce` might be illogical and could potentially lead to this or other errors depending on internal implementation, although this specific error checks for identical behavior names).

## Solution

Review the binding expression identified in the error message and remove the duplicate binding behavior application. Ensure that each desired behavior is listed only once using the `&` syntax.

## Example

```html
<!-- Incorrect: 'debounce' is applied twice -->
<input value.bind="searchTerm & debounce:500 & debounce:500">

<!-- Incorrect: 'throttle' is applied twice -->
<div mousemove.trigger="handleMouseMove($event) & throttle:100 & throttle:100"></div>

<!-- Correct: Apply each behavior only once -->
<input value.bind="searchTerm & debounce:500">
<div mousemove.trigger="handleMouseMove($event) & throttle:100"></div>

<!-- Example with multiple *different* behaviors (Correct) -->
<input value.bind="searchTerm & debounce:500 & updateTrigger:'blur'">
```

## Debugging Tips

* Carefully read the binding expression in your template where the error is reported.
* Look for repeated `& behaviorName` segments.
* Ensure you haven't accidentally copied and pasted parts of the binding expression leading to duplication.


---

# Agent Instructions
This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com.

## Querying This Documentation
If you need additional information that is not directly available in this page, you can query the documentation by asking a question.

Perform an HTTP GET request on the following URL with the `ask` and `goal` query parameters:

```
GET https://docs.aurelia.io/developer-guides/error-messages/runtime-html/aur0102.md?ask=<question>&goal=<user_goal>
```

`ask` is the immediate question: it should be specific, self-contained, and written in natural language.
`goal` is what the user is ultimately trying to achieve, the reason they need the answer. Sharing it helps GitBook give you a better, more relevant answer. A goal is most helpful when it describes the outcome the user wants rather than restating the question. For example, with `ask=how do I create an API token`, a goal like `automate deployments from our CI pipeline` lets GitBook tailor the answer to that use case.

The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.