# AUR0174

## Error Message

`AUR0174: Expression error: arrow function with default parameters is not supported: "{{expression}}"`

## Description

Aurelia binding expressions do not support arrow functions with default parameter values.

## Example Trigger

```html
<!-- ❌ Default parameter -->
<div textcontent.bind="(a = 1) => a + 1"></div>
```

## Solution

* Remove default parameters and implement defaults in view-model code.