AUR0199

Error Message

AUR0199: Trying to observe property {{property}} on null/undefined

Where {{property}} is the property key Aurelia attempted to observe.

Description

This error occurs when Aurelia’s observation system is asked to observe a property on a null or undefined object.

Common Scenarios

<!-- ❌ user is null/undefined -->
<template>
  <input value.bind="user.name">
</template>

export class MyVm {
  user: { name: string } | null = null;
}

Solutions

• Initialize objects before binding to their properties.

• Guard bindings with if.bind until the object exists.

<!-- ✅ Guard -->
<template>
  <div if.bind="user">
    <input value.bind="user.name">
  </div>
</template>

Troubleshooting

• Check the stack trace to see which binding attempted to observe {{property}}.

• Log the binding context object to confirm it is not null/undefined at bind time.