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

title	generated
Compiler warnings	generated by process-messages/index.js

Svelte warns you at compile time if it catches potential mistakes, such as writing inaccessible markup.

Some warnings may be incorrect in your concrete use case. You can disable such false positives by placing a <!-- svelte-ignore <code> --> comment above the line that causes the warning. Example:

<!-- svelte-ignore a11y_autofocus -->
<input autofocus />

You can list multiple rules in a single comment, and add an explanatory note alongside them:

<!-- svelte-ignore a11y_click_events_have_key_events, a11y_no_static_element_interactions (because of reasons) -->
<div on:click>...</div>

a11y_accesskey

[!NOTE] Avoid using accesskey

a11y_aria_activedescendant_has_tabindex

[!NOTE] An element with an aria-activedescendant attribute should have a tabindex value

a11y_aria_attributes

[!NOTE] '<%name%>' should not have aria-* attributes

a11y_autocomplete_valid

[!NOTE] '%value%' is an invalid value for 'autocomplete' on '<input type="%type%">'

a11y_autofocus

[!NOTE] Avoid using autofocus

a11y_click_events_have_key_events

[!NOTE] Visible, non-interactive elements with a click event must be accompanied by a keyboard event handler. Consider whether an interactive element such as '<button type="button">' or '<a>' might be more appropriate. See https://svelte.dev/docs/accessibility-warnings#a11y-click-events-have-key-events for more details

a11y_consider_explicit_label

[!NOTE] Buttons and links should either contain text or have an 'aria-label' or 'aria-labelledby' attribute

a11y_distracting_elements

[!NOTE] Avoid '<%name%>' elements

a11y_figcaption_index

[!NOTE] '<figcaption>' must be first or last child of '<figure>'

a11y_figcaption_parent

[!NOTE] '<figcaption>' must be an immediate child of '<figure>'

a11y_hidden

[!NOTE] '<%name%>' element should not be hidden

a11y_img_redundant_alt

[!NOTE] Screenreaders already announce '<img>' elements as an image

a11y_incorrect_aria_attribute_type

[!NOTE] The value of '%attribute%' must be a %type%

a11y_incorrect_aria_attribute_type_boolean

[!NOTE] The value of '%attribute%' must be either 'true' or 'false'. It cannot be empty

a11y_incorrect_aria_attribute_type_id

[!NOTE] The value of '%attribute%' must be a string that represents a DOM element ID

a11y_incorrect_aria_attribute_type_idlist

[!NOTE] The value of '%attribute%' must be a space-separated list of strings that represent DOM element IDs

a11y_incorrect_aria_attribute_type_integer

[!NOTE] The value of '%attribute%' must be an integer

a11y_incorrect_aria_attribute_type_token

[!NOTE] The value of '%attribute%' must be exactly one of %values%

a11y_incorrect_aria_attribute_type_tokenlist

[!NOTE] The value of '%attribute%' must be a space-separated list of one or more of %values%

a11y_incorrect_aria_attribute_type_tristate

[!NOTE] The value of '%attribute%' must be exactly one of true, false, or mixed

a11y_interactive_supports_focus

[!NOTE] Elements with the '%role%' interactive role must have a tabindex value

a11y_invalid_attribute

[!NOTE] '%href_value%' is not a valid %href_attribute% attribute

a11y_label_has_associated_control

[!NOTE] A form label must be associated with a control

a11y_media_has_caption

[!NOTE] '<video>' elements must have a '<track kind="captions">'

a11y_misplaced_role

[!NOTE] '<%name%>' should not have role attribute

a11y_misplaced_scope

[!NOTE] The scope attribute should only be used with '<th>' elements

a11y_missing_attribute

[!NOTE] '<%name%>' element should have %article% %sequence% attribute

a11y_missing_content

[!NOTE] '<%name%>' element should contain text

a11y_mouse_events_have_key_events

[!NOTE] '%event%' event must be accompanied by '%accompanied_by%' event

a11y_no_abstract_role

[!NOTE] Abstract role '%role%' is forbidden

a11y_no_interactive_element_to_noninteractive_role

[!NOTE] '<%element%>' cannot have role '%role%'

a11y_no_noninteractive_element_interactions

[!NOTE] Non-interactive element '<%element%>' should not be assigned mouse or keyboard event listeners

a11y_no_noninteractive_element_to_interactive_role

[!NOTE] Non-interactive element '<%element%>' cannot have interactive role '%role%'

a11y_no_noninteractive_tabindex

[!NOTE] noninteractive element cannot have nonnegative tabIndex value

a11y_no_redundant_roles

[!NOTE] Redundant role '%role%'

a11y_no_static_element_interactions

[!NOTE] '<%element%>' with a %handler% handler must have an ARIA role

a11y_positive_tabindex

[!NOTE] Avoid tabindex values above zero

a11y_role_has_required_aria_props

[!NOTE] Elements with the ARIA role "%role%" must have the following attributes defined: %props%

a11y_role_supports_aria_props

[!NOTE] The attribute '%attribute%' is not supported by the role '%role%'

a11y_role_supports_aria_props_implicit

[!NOTE] The attribute '%attribute%' is not supported by the role '%role%'. This role is implicit on the element '<%name%>'

a11y_unknown_aria_attribute

[!NOTE] Unknown aria attribute 'aria-%attribute%'

[!NOTE] Unknown aria attribute 'aria-%attribute%'. Did you mean '%suggestion%'?

a11y_unknown_role

[!NOTE] Unknown role '%role%'

[!NOTE] Unknown role '%role%'. Did you mean '%suggestion%'?

attribute_avoid_is

[!NOTE] The "is" attribute is not supported cross-browser and should be avoided

attribute_global_event_reference

[!NOTE] You are referencing 'globalThis.%name%'. Did you forget to declare a variable with that name?

attribute_illegal_colon

[!NOTE] Attributes should not contain ':' characters to prevent ambiguity with Svelte directives

attribute_invalid_property_name

[!NOTE] '%wrong%' is not a valid HTML attribute. Did you mean '%right%'?

attribute_quoted

[!NOTE] Quoted attributes on components and custom elements will be stringified in a future version of Svelte. If this isn't what you want, remove the quotes

bind_invalid_each_rest

[!NOTE] The rest operator (...) will create a new object and binding '%name%' with the original object will not work

block_empty

[!NOTE] Empty block

component_name_lowercase

[!NOTE] '<%name%>' will be treated as an HTML element unless it begins with a capital letter

css_unused_selector

[!NOTE] Unused CSS selector "%name%"

element_invalid_self_closing_tag

[!NOTE] Self-closing HTML tags for non-void elements are ambiguous — use '<%name% ...></%name%>' rather than '<%name% ... />'

event_directive_deprecated

[!NOTE] Using 'on:%name%' to listen to the %name% event is deprecated. Use the event attribute 'on%name%' instead

export_let_unused

[!NOTE] Component has unused export property '%name%'. If it is for external reference only, please consider using 'export const %name%'

legacy_code

[!NOTE] '%code%' is no longer valid — please use '%suggestion%' instead

legacy_component_creation

[!NOTE] Svelte 5 components are no longer classes. Instantiate them using 'mount' or 'hydrate' (imported from 'svelte') instead.

node_invalid_placement_ssr

[!NOTE] %thing% is invalid inside '<%parent%>'. When rendering this component on the server, the resulting HTML will be modified by the browser, likely resulting in a 'hydration_mismatch' warning

HTML restricts where certain elements can appear. In case of a violation the browser will 'repair' the HTML in a way that breaks Svelte's assumptions about the structure of your components. Some examples:

• <p>hello <div>world</div></p> will result in <p>hello </p><div>world</div><p></p> for example (the <div> autoclosed the <p> because <p> cannot contain block-level elements)
• <option><div>option a</div></option> will result in <option>option a</option> (the <div> is removed)
• <table><tr><td>cell</td></tr></table> will result in <table><tbody><tr><td>cell</td></tr></tbody></table> (a <tbody> is auto-inserted)

This code will work when the component is rendered on the client (which is why this is a warning rather than an error), but if you use server rendering it will cause hydration to fail.

non_reactive_update

[!NOTE] '%name%' is updated, but is not declared with '$state(...)'. Changing its value will not correctly trigger updates

options_deprecated_accessors

[!NOTE] The 'accessors' option has been deprecated. It will have no effect in runes mode

options_deprecated_immutable

[!NOTE] The 'immutable' option has been deprecated. It will have no effect in runes mode

options_missing_custom_element

[!NOTE] The 'customElement' option is used when generating a custom element. Did you forget the 'customElement: true' compile option?

options_removed_enable_sourcemap

[!NOTE] The 'enableSourcemap' option has been removed. Source maps are always generated now, and tooling can choose to ignore them

options_removed_hydratable

[!NOTE] The 'hydratable' option has been removed. Svelte components are always hydratable now

options_removed_loop_guard_timeout

[!NOTE] The 'loopGuardTimeout' option has been removed

options_renamed_ssr_dom

[!NOTE] 'generate: "dom"' and 'generate: "ssr"' options have been renamed to "client" and "server" respectively

perf_avoid_inline_class

[!NOTE] Avoid 'new class' — instead, declare the class at the top level scope

perf_avoid_nested_class

[!NOTE] Avoid declaring classes below the top level scope

reactive_declaration_invalid_placement

[!NOTE] Reactive declarations only exist at the top level of the instance script

reactive_declaration_module_script_dependency

[!NOTE] Reassignments of module-level declarations will not cause reactive statements to update

reactive_declaration_non_reactive_property

[!NOTE] Properties of objects and arrays are not reactive unless in runes mode. Changes to this property will not cause the reactive statement to update

script_context_deprecated

[!NOTE] 'context="module"' is deprecated, use the 'module' attribute instead

script_unknown_attribute

[!NOTE] Unrecognized attribute — should be one of 'generics', 'lang' or 'module'. If this exists for a preprocessor, ensure that the preprocessor removes it

slot_element_deprecated

[!NOTE] Using '<slot>' to render parent content is deprecated. Use '{@render ...}' tags instead

state_referenced_locally

[!NOTE] State referenced in its own scope will never update. Did you mean to reference it inside a closure?

store_rune_conflict

[!NOTE] It looks like you're using the '%name%' rune, but there is a local binding called '%name%'. Referencing a local variable with a '' prefix will create a store subscription. Please rename '%name%' to avoid the ambiguity

svelte_component_deprecated

[!NOTE] '<svelte:component>' is deprecated in runes mode — components are dynamic by default

In previous versions of Svelte, the component constructor was fixed when the component was rendered. In other words, if you wanted <X> to re-render when X changed, you would either have to use <svelte:component this={X}> or put the component inside a {#key X}...{/key} block.

In Svelte 5 this is no longer true — if X changes, <X> re-renders.

In some cases <object.property> syntax can be used as a replacement; a lowercased variable with property access is recognized as a component in Svelte 5.

For complex component resolution logic, an intermediary, capitalized variable may be necessary. E.g. in places where @const can be used:

{#each items as item}
-	<svelte:component this={item.condition ? Y : Z} />
+	{@const Component = item.condition ? Y : Z}
+	<Component />
{/each}

A derived value may be used in other contexts:

<script>
	...
	let condition = $state(false);
+	const Component = $derived(condition ? Y : Z);
</script>
- <svelte:component this={condition ? Y : Z} />
+ <Component />

svelte_element_invalid_this

[!NOTE] 'this' should be an '{expression}'. Using a string attribute value will cause an error in future versions of Svelte

svelte_self_deprecated

[!NOTE] '<svelte:self>' is deprecated — use self-imports (e.g. 'import %name% from './%basename%'') instead

unknown_code

[!NOTE] '%code%' is not a recognised code

[!NOTE] '%code%' is not a recognised code (did you mean '%suggestion%'?)