svelte/documentation/docs/98-reference/.generated/client-errors.md

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### bind_invalid_checkbox_value

```
Using `bind:value` together with a checkbox input is not allowed. Use `bind:checked` instead
```

### bind_invalid_export

```
Component %component% has an export named `%key%` that a consumer component is trying to access using `bind:%key%`, which is disallowed. Instead, use `bind:this` (e.g. `<%name% bind:this={component} />`) and then access the property on the bound component instance (e.g. `component.%key%`)
```

### bind_not_bindable

```
A component is attempting to bind to a non-bindable property `%key%` belonging to %component% (i.e. `<%name% bind:%key%={...}>`). To mark a property as bindable: `let { %key% = $bindable() } = $props()`
```

### component_api_changed

```
%parent% called `%method%` on an instance of %component%, which is no longer valid in Svelte 5
```

See the [migration guide](/docs/svelte/v5-migration-guide#Components-are-no-longer-classes) for more information.

### component_api_invalid_new

```
Attempted to instantiate %component% with `new %name%`, which is no longer valid in Svelte 5. If this component is not under your control, set the `compatibility.componentApi` compiler option to `4` to keep it working.
```

See the [migration guide](/docs/svelte/v5-migration-guide#Components-are-no-longer-classes) for more information.

### derived_references_self

```
A derived value cannot reference itself recursively
```

### each_key_duplicate

```
Keyed each block has duplicate key at indexes %a% and %b%
```

```
Keyed each block has duplicate key `%value%` at indexes %a% and %b%
```

### effect_in_teardown

```
`%rune%` cannot be used inside an effect cleanup function
```

### effect_in_unowned_derived

```
Effect cannot be created inside a `$derived` value that was not itself created inside an effect
```

### effect_orphan

```
`%rune%` can only be used inside an effect (e.g. during component initialisation)
```

### effect_update_depth_exceeded

```
Maximum update depth exceeded. This can happen when a reactive block or effect repeatedly sets a new value. Svelte limits the number of nested updates to prevent infinite loops
```

### hydration_failed

```
Failed to hydrate the application
```

### invalid_snippet

```
Could not `{@render}` snippet due to the expression being `null` or `undefined`. Consider using optional chaining `{@render snippet?.()}`
```

### lifecycle_legacy_only

```
`%name%(...)` cannot be used in runes mode
```

### props_invalid_value

```
Cannot do `bind:%key%={undefined}` when `%key%` has a fallback value
```

### props_rest_readonly

```
Rest element properties of `$props()` such as `%property%` are readonly
```

### rune_outside_svelte

```
The `%rune%` rune is only available inside `.svelte` and `.svelte.js/ts` files
```

### state_descriptors_fixed

```
Property descriptors defined on `$state` objects must contain `value` and always be `enumerable`, `configurable` and `writable`.
```

### state_prototype_fixed

```
Cannot set prototype of `$state` object
```

### state_unsafe_mutation

```
Updating state inside a derived or a template expression is forbidden. If the value should not be reactive, declare it without `$state`
```

This error is thrown in a situation like this:

```svelte
<script>
    let count = $state(0);
    let multiple = $derived.by(() => {
        const result = count * 2;
        if (result > 10) {
            count = 0;
        }
        return result;
    });
</script>

<button onclick={() => count++}>{count} / {multiple}</button>
```

Here, the `$derived` updates `count`, which is `$state` and therefore forbidden to do. It is forbidden because the reactive graph could become unstable as a result, leading to subtle bugs, like values being stale or effects firing in the wrong order. To prevent this, Svelte errors when detecting an update to a `$state` variable.

To fix this:
- See if it's possible to refactor your `$derived` such that the update becomes unnecessary
- Think about why you need to update `$state` inside a `$derived` in the first place. Maybe it's because you're using `bind:`, which leads you down a bad code path, and separating input and output path (by splitting it up to an attribute and an event, or by using [Function bindings](bind#Function-bindings)) makes it possible avoid the update
- If it's unavoidable, you may need to use an [`$effect`]($effect) instead. This could include splitting parts of the `$derived` into an [`$effect`]($effect) which does the updates