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

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

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%'?)