svelte/documentation/docs/98-reference/30-runtime-warnings.md

---
title: 'Runtime warnings'
generated: 'generated by process-messages/index.js'
---

## `binding_property_non_reactive`

> [!NOTE] '%binding%' is binding to a non-reactive property

> [!NOTE] '%binding%' (%location%) is binding to a non-reactive property

## `console_log_state`

> [!NOTE] Your 'console.%method%' contained '$state' proxies. Consider using '$inspect(...)' or '$state.snapshot(...)' instead

When logging a [proxy](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Proxy), browser devtools will log the proxy itself rather than the value it represents. In the case of Svelte, the 'target' of a `$state` proxy might not resemble its current value, which can be confusing.

The easiest way to log a value as it changes over time is to use the [`$inspect`](https://svelte-5-preview.vercel.app/docs/runes#$inspect) rune. Alternatively, to log things on a one-off basis (for example, inside an event handler) you can use [`$state.snapshot`](https://svelte-5-preview.vercel.app/docs/runes#$state-snapshot) to take a snapshot of the current value.

## `dynamic_void_element_content`

> [!NOTE] '\<svelte:element this="%tag%">' is a void element — it cannot have content

## `event_handler_invalid`

> [!NOTE] %handler% should be a function. Did you mean to %suggestion%?

## `hydration_attribute_changed`

> [!NOTE] The '%attribute%' attribute on '%html%' changed its value between server and client renders. The client value, '%value%', will be ignored in favour of the server value

## `hydration_html_changed`

> [!NOTE] The value of an '{@html ...}' block changed between server and client renders. The client value will be ignored in favour of the server value

> [!NOTE] The value of an '{@html ...}' block %location% changed between server and client renders. The client value will be ignored in favour of the server value

## `hydration_mismatch`

> [!NOTE] Hydration failed because the initial UI does not match what was rendered on the server

> [!NOTE] Hydration failed because the initial UI does not match what was rendered on the server. The error occurred near %location%

## `invalid_raw_snippet_render`

> [!NOTE] The 'render' function passed to 'createRawSnippet' should return HTML for a single element

## `lifecycle_double_unmount`

> [!NOTE] Tried to unmount a component that was not mounted

## `ownership_invalid_binding`

> [!NOTE] %parent% passed a value to %child% with 'bind:', but the value is owned by %owner%. Consider creating a binding between %owner% and %parent%

## `ownership_invalid_mutation`

> [!NOTE] Mutating a value outside the component that created it is strongly discouraged. Consider passing values to child components with 'bind:', or use a callback instead

> [!NOTE] %component% mutated a value owned by %owner%. This is strongly discouraged. Consider passing values to child components with 'bind:', or use a callback instead

## `state_proxy_equality_mismatch`

> [!NOTE] Reactive '$state(...)' proxies and the values they proxy have different identities. Because of this, comparisons with '%operator%' will produce unexpected results

`$state(...)` creates a [proxy](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Proxy) of the value it is passed. The proxy and the value have different identities, meaning equality checks will always return `false`:

```svelte
<script>
	let value = { foo: 'bar' };
	let proxy = $state(value);

	value === proxy; // always false
</script>
```

To resolve this, ensure you're comparing values where both values were created with `$state(...)`, or neither were. Note that `$state.raw(...)` will _not_ create a state proxy.

## `state_snapshot_uncloneable`

> [!NOTE] Value cannot be cloned with '$state.snapshot' — the original value was returned

> [!NOTE] The following properties cannot be cloned with '$state.snapshot' — the return value contains the originals:
> %properties%