SvelteReference

Compiler warnings

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  comment above the line that causes the warning. Example:

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

You can list multiple rules in a single comment (separated by commas), and add an explanatory note (in parentheses) alongside them:

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

a11y_accesskey

Avoid using accesskey

Enforce no accesskey on element. Access keys are HTML attributes that allow web developers to assign keyboard shortcuts to elements. Inconsistencies between keyboard shortcuts and keyboard commands used by screen reader and keyboard-only users create accessibility complications. To avoid complications, access keys should not be used.

<!-- A11y: Avoid using accesskey -->
<div accesskey="z"></div>

a11y_aria_activedescendant_has_tabindex

An element with an aria-activedescendant attribute should have a tabindex value

An element with aria-activedescendant must be tabbable, so it must either have an inherent tabindex or declare tabindex as an attribute.

<!-- A11y: Elements with attribute aria-activedescendant should have tabindex value -->
<div aria-activedescendant="some-id"></div>

a11y_aria_attributes

`<%name%>` should not have aria-* attributes

Certain reserved DOM elements do not support ARIA roles, states and properties. This is often because they are not visible, for example meta, html, script, style. This rule enforces that these DOM elements do not contain the aria-* props.

<!-- A11y: <meta> should not have aria-* attributes -->
<meta aria-hidden="false" />

a11y_autocomplete_valid

'%value%' is an invalid value for 'autocomplete' on `<input type="%type%">`

a11y_autofocus

Avoid using autofocus

Enforce that autofocus is not used on elements. Autofocusing elements can cause usability issues for sighted and non-sighted users alike.

<!-- A11y: Avoid using autofocus -->
<input autofocus />

a11y_click_events_have_key_events

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

Enforce that visible, non-interactive elements with an onclick event are accompanied by a keyboard event handler.

Users should first consider whether an interactive element might be more appropriate such as a <button type="button"> element for actions or <a> element for navigations. These elements are more semantically meaningful and will have built-in key handling. E.g. Space and Enter will trigger a <button> and Enter will trigger an <a> element.

If a non-interactive element is required then onclick should be accompanied by an onkeyup or onkeydown handler that enables the user to perform equivalent actions via the keyboard. In order for the user to be able to trigger a key press, the element will also need to be focusable by adding a tabindex. While an onkeypress handler will also silence this warning, it should be noted that the keypress event is deprecated.

<!-- A11y: visible, non-interactive elements with an onclick event must be accompanied by a keyboard event handler. -->
<div onclick={() => {}}></div>

Coding for the keyboard is important for users with physical disabilities who cannot use a mouse, AT compatibility, and screenreader users.

a11y_consider_explicit_label

Buttons and links should either contain text or have an `aria-label` or `aria-labelledby` attribute

a11y_distracting_elements

Avoid `<%name%>` elements

Enforces that no distracting elements are used. Elements that can be visually distracting can cause accessibility issues with visually impaired users. Such elements are most likely deprecated, and should be avoided.

The following elements are visually distracting: <marquee> and <blink>.

<!-- A11y: Avoid <marquee> elements -->
<marquee></marquee>

a11y_figcaption_index

`<figcaption>` must be first or last child of `<figure>`

a11y_figcaption_parent

`<figcaption>` must be an immediate child of `<figure>`

Enforce that certain DOM elements have the correct structure.

<!-- A11y: <figcaption> must be an immediate child of <figure> -->
<div>
	<figcaption>Image caption</figcaption>
</div>

a11y_hidden

`<%name%>` element should not be hidden

Certain DOM elements are useful for screen reader navigation and should not be hidden.

<!-- A11y: <h2> element should not be hidden -->
<h2 aria-hidden="true">invisible header</h2>

a11y_img_redundant_alt

Screenreaders already announce `<img>` elements as an image

Enforce img alt attribute does not contain the word image, picture, or photo. Screen readers already announce img elements as an image. There is no need to use words such as image, photo, and/or picture.

<img src="foo" alt="Foo eating a sandwich." />

<!-- aria-hidden, won't be announced by screen reader -->
<img src="bar" aria-hidden="true" alt="Picture of me taking a photo of an image" />

<!-- A11y: Screen readers already announce <img> elements as an image. -->
<img src="foo" alt="Photo of foo being weird." />

<!-- A11y: Screen readers already announce <img> elements as an image. -->
<img src="bar" alt="Image of me at a bar!" />

<!-- A11y: Screen readers already announce <img> elements as an image. -->
<img src="foo" alt="Picture of baz fixing a bug." />

a11y_incorrect_aria_attribute_type

The value of '%attribute%' must be a %type%

Enforce that only the correct type of value is used for aria attributes. For example, aria-hidden should only receive a boolean.

<!-- A11y: The value of 'aria-hidden' must be exactly one of true or false -->
<div aria-hidden="yes"></div>

a11y_incorrect_aria_attribute_type_boolean

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

a11y_incorrect_aria_attribute_type_id

The value of '%attribute%' must be a string that represents a DOM element ID

a11y_incorrect_aria_attribute_type_idlist

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

a11y_incorrect_aria_attribute_type_integer

The value of '%attribute%' must be an integer

a11y_incorrect_aria_attribute_type_token

The value of '%attribute%' must be exactly one of %values%

a11y_incorrect_aria_attribute_type_tokenlist

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

a11y_incorrect_aria_attribute_type_tristate

The value of '%attribute%' must be exactly one of true, false, or mixed

a11y_interactive_supports_focus

Elements with the '%role%' interactive role must have a tabindex value

Enforce that elements with an interactive role and interactive handlers (mouse or key press) must be focusable or tabbable.

<!-- A11y: Elements with the 'button' interactive role must have a tabindex value. -->
<div role="button" onkeypress={() => {}} />

a11y_invalid_attribute

'%href_value%' is not a valid %href_attribute% attribute

Enforce that attributes important for accessibility have a valid value. For example, href should not be empty, '#', or javascript:.

<!-- A11y: '' is not a valid href attribute -->
<a href="">invalid</a>

a11y_label_has_associated_control

A form label must be associated with a control

Enforce that a label tag has a text label and an associated control.

There are two supported ways to associate a label with a control:

Wrapping a control in a label tag.
Adding for to a label and assigning it the ID of an input on the page.

<label for="id">B</label>

<label>C <input type="text" /></label>

<!-- A11y: A form label must be associated with a control. -->
<label>A</label>

a11y_media_has_caption

`<video>` elements must have a `<track kind="captions">`

Providing captions for media is essential for deaf users to follow along. Captions should be a transcription or translation of the dialogue, sound effects, relevant musical cues, and other relevant audio information. Not only is this important for accessibility, but can also be useful for all users in the case that the media is unavailable (similar to alt text on an image when an image is unable to load).

The captions should contain all important and relevant information to understand the corresponding media. This may mean that the captions are not a 1:1 mapping of the dialogue in the media content. However, captions are not necessary for video components with the muted attribute.

<video><track kind="captions" /></video>

<audio muted></audio>

<!-- A11y: Media elements must have a <track kind=\"captions\"> -->
<video></video>

<!-- A11y: Media elements must have a <track kind=\"captions\"> -->
<video><track /></video>

a11y_misplaced_role

`<%name%>` should not have role attribute

<!-- A11y: <meta> should not have role attribute -->
<meta role="tooltip" />

a11y_misplaced_scope

The scope attribute should only be used with `<th>` elements

The scope attribute should only be used on <th> elements.

<!-- A11y: The scope attribute should only be used with <th> elements -->
<div scope="row" />

a11y_missing_attribute

`<%name%>` element should have %article% %sequence% attribute

Enforce that attributes required for accessibility are present on an element. This includes the following checks:

<a> should have an href (unless it’s a fragment-defining tag)
<area> should have alt, aria-label, or aria-labelledby
<html> should have lang
<iframe> should have title
<img> should have alt
<object> should have title, aria-label, or aria-labelledby
<input type="image"> should have alt, aria-label, or aria-labelledby

<!-- A11y: <input type=\"image\"> element should have an alt, aria-label or aria-labelledby attribute -->
<input type="image" />

<!-- A11y: <html> element should have a lang attribute -->
<html></html>

<!-- A11y: <a> element should have an href attribute -->
<a>text</a>

a11y_missing_content

`<%name%>` element should contain text

Enforce that heading elements (h1, h2, etc.) and anchors have content and that the content is accessible to screen readers

<!-- A11y: <a> element should have child content -->
<a href="/foo"></a>

<!-- A11y: <h1> element should have child content -->
<h1></h1>

a11y_mouse_events_have_key_events

'%event%' event must be accompanied by '%accompanied_by%' event

Enforce that onmouseover and onmouseout are accompanied by onfocus and onblur, respectively. This helps to ensure that any functionality triggered by these mouse events is also accessible to keyboard users.

<!-- A11y: onmouseover must be accompanied by onfocus -->
<div onmouseover={handleMouseover} />

<!-- A11y: onmouseout must be accompanied by onblur -->
<div onmouseout={handleMouseout} />

a11y_no_abstract_role

Abstract role '%role%' is forbidden

a11y_no_interactive_element_to_noninteractive_role

`<%element%>` cannot have role '%role%'

WAI-ARIA roles should not be used to convert an interactive element to a non-interactive element. Non-interactive ARIA roles include article, banner, complementary, img, listitem, main, region and tooltip.

<!-- A11y: <textarea> cannot have role 'listitem' -->
<textarea role="listitem"></textarea>

a11y_no_noninteractive_element_interactions

Non-interactive element `<%element%>` should not be assigned mouse or keyboard event listeners

A non-interactive element does not support event handlers (mouse and key handlers). Non-interactive elements include <main>, <area>, <h1> (,<h2>, etc), <p>, <img>, <li>, <ul> and <ol>. Non-interactive WAI-ARIA roles include article, banner, complementary, img, listitem, main, region and tooltip.

<!-- `A11y: Non-interactive element <li> should not be assigned mouse or keyboard event listeners.` -->
<li onclick={() => {}}></li>

<!-- `A11y: Non-interactive element <div> should not be assigned mouse or keyboard event listeners.` -->
<div role="listitem" onclick={() => {}}></div>

a11y_no_noninteractive_element_to_interactive_role

Non-interactive element `<%element%>` cannot have interactive role '%role%'

WAI-ARIA roles should not be used to convert a non-interactive element to an interactive element. Interactive ARIA roles include button, link, checkbox, menuitem, menuitemcheckbox, menuitemradio, option, radio, searchbox, switch and textbox.

<!-- A11y: Non-interactive element <h3> cannot have interactive role 'searchbox' -->
<h3 role="searchbox">Button</h3>

a11y_no_noninteractive_tabindex

noninteractive element cannot have nonnegative tabIndex value

Tab key navigation should be limited to elements on the page that can be interacted with.

<!-- A11y: noninteractive element cannot have nonnegative tabIndex value -->
<div tabindex="0"></div>

a11y_no_redundant_roles

Redundant role '%role%'

Some HTML elements have default ARIA roles. Giving these elements an ARIA role that is already set by the browser has no effect and is redundant.

<!-- A11y: Redundant role 'button' -->
<button role="button">...</button>

<!-- A11y: Redundant role 'img' -->
<img role="img" src="foo.jpg" />

a11y_no_static_element_interactions

`<%element%>` with a %handler% handler must have an ARIA role

Elements like <div> with interactive handlers like click must have an ARIA role.

<!-- A11y: <div> with click handler must have an ARIA role -->
<div onclick={() => ''}></div>

a11y_positive_tabindex

Avoid tabindex values above zero

Avoid positive tabindex property values. This will move elements out of the expected tab order, creating a confusing experience for keyboard users.

<!-- A11y: avoid tabindex values above zero -->
<div tabindex="1"></div>

a11y_role_has_required_aria_props

Elements with the ARIA role "%role%" must have the following attributes defined: %props%

Elements with ARIA roles must have all required attributes for that role.

<!-- A11y: A11y: Elements with the ARIA role "checkbox" must have the following attributes defined: "aria-checked" -->
<span role="checkbox" aria-labelledby="foo" tabindex="0"></span>

a11y_role_supports_aria_props

The attribute '%attribute%' is not supported by the role '%role%'

Elements with explicit or implicit roles defined contain only aria-* properties supported by that role.

<!-- A11y: The attribute 'aria-multiline' is not supported by the role 'link'. -->
<div role="link" aria-multiline></div>

<!-- A11y: The attribute 'aria-required' is not supported by the role 'listitem'. This role is implicit on the element <li>. -->
<li aria-required></li>

a11y_role_supports_aria_props_implicit

The attribute '%attribute%' is not supported by the role '%role%'. This role is implicit on the element `<%name%>`

Elements with explicit or implicit roles defined contain only aria-* properties supported by that role.

<!-- A11y: The attribute 'aria-multiline' is not supported by the role 'link'. -->
<div role="link" aria-multiline></div>

<!-- A11y: The attribute 'aria-required' is not supported by the role 'listitem'. This role is implicit on the element <li>. -->
<li aria-required></li>

a11y_unknown_aria_attribute

Unknown aria attribute 'aria-%attribute%'

Unknown aria attribute 'aria-%attribute%'. Did you mean '%suggestion%'?

Enforce that only known ARIA attributes are used. This is based on the WAI-ARIA States and Properties spec.

<!-- A11y: Unknown aria attribute 'aria-labeledby' (did you mean 'labelledby'?) -->
<input type="image" aria-labeledby="foo" />

a11y_unknown_role

Unknown role '%role%'

Unknown role '%role%'. Did you mean '%suggestion%'?

Elements with ARIA roles must use a valid, non-abstract ARIA role. A reference to role definitions can be found at WAI-ARIA site.

<!-- A11y: Unknown role 'toooltip' (did you mean 'tooltip'?) -->
<div role="toooltip"></div>

attribute_avoid_is

The "is" attribute is not supported cross-browser and should be avoided

attribute_global_event_reference

You are referencing `globalThis.%name%`. Did you forget to declare a variable with that name?

attribute_illegal_colon

Attributes should not contain ':' characters to prevent ambiguity with Svelte directives

attribute_invalid_property_name

'%wrong%' is not a valid HTML attribute. Did you mean '%right%'?

attribute_quoted

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

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

block_empty

Empty block

component_name_lowercase

`<%name%>` will be treated as an HTML element unless it begins with a capital letter

css_unused_selector

Unused CSS selector "%name%"

Svelte traverses both the template and the <style> tag to find out which of the CSS selectors are not used within the template, so it can remove them.

In some situations a selector may target an element that is not ‘visible’ to the compiler, for example because it is part of an {@html ...} tag or you’re overriding styles in a child component. In these cases, use :global to preserve the selector as-is:

<div class="post">{@html content}</div>

<style>
  .post :global {
	p {...}
  }
</style>

element_invalid_self_closing_tag

Self-closing HTML tags for non-void elements are ambiguous — use `<%name% ...></%name%>` rather than `<%name% ... />`

event_directive_deprecated

Using `on:%name%` to listen to the %name% event is deprecated. Use the event attribute `on%name%` instead

See the migration guide for more info.

export_let_unused

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

legacy_code

`%code%` is no longer valid — please use `%suggestion%` instead

legacy_component_creation

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

See the migration guide for more info.

node_invalid_placement_ssr

%message%. When rendering this component on the server, the resulting HTML will be modified by the browser (by moving, removing, or inserting elements), 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> (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

`%name%` is updated, but is not declared with `$state(...)`. Changing its value will not correctly trigger updates

This warning is thrown when the compiler detects the following:

a variable was declared without $state or $state.raw
the variable is reassigned
the variable is read in a reactive context

In this case, changing the value will not correctly trigger updates. Example:

<script>
	let reactive = $state('reactive');
	let stale = 'stale';
</script>

<p>This value updates: {reactive}</p>
<p>This value does not update: {stale}</p>

<button onclick={() => {
	stale = 'updated';
	reactive = 'updated';
}}>update</button>

To fix this, wrap your variable declaration with $state.

options_deprecated_accessors

The `accessors` option has been deprecated. It will have no effect in runes mode

options_deprecated_immutable

The `immutable` option has been deprecated. It will have no effect in runes mode

options_missing_custom_element

The `customElement` option is used when generating a custom element. Did you forget the `customElement: true` compile option?

options_removed_enable_sourcemap

The `enableSourcemap` option has been removed. Source maps are always generated now, and tooling can choose to ignore them

options_removed_hydratable

The `hydratable` option has been removed. Svelte components are always hydratable now

options_removed_loop_guard_timeout

The `loopGuardTimeout` option has been removed

options_renamed_ssr_dom

`generate: "dom"` and `generate: "ssr"` options have been renamed to "client" and "server" respectively

perf_avoid_inline_class

Avoid 'new class' — instead, declare the class at the top level scope

perf_avoid_nested_class

Avoid declaring classes below the top level scope

reactive_declaration_invalid_placement

Reactive declarations only exist at the top level of the instance script

reactive_declaration_module_script_dependency

Reassignments of module-level declarations will not cause reactive statements to update

script_context_deprecated

`context="module"` is deprecated, use the `module` attribute instead

<script context="module" module>
	let foo = 'bar';
</script>

script_unknown_attribute

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

Using `<slot>` to render parent content is deprecated. Use `{@render ...}` tags instead

See the migration guide for more info.

state_referenced_locally

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

This warning is thrown when the compiler detects the following:

A reactive variable is declared
the variable is reassigned
the variable is referenced inside the same scope it is declared and it is a non-reactive context

In this case, the state reassignment will not be noticed by whatever you passed it to. For example, if you pass the state to a function, that function will not notice the updates:

Parent

<script>
	import { setContext } from 'svelte';

	let count = $state(0);

	// warning: state_referenced_locally
	setContext('count', count);
</script>

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

<script lang="ts">
	import { setContext } from 'svelte';

	let count = $state(0);

	// warning: state_referenced_locally
	setContext('count', count);
</script>

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

Child

<script>
	import { getContext } from 'svelte';

	const count = getContext('count');
</script>

<!-- This will never update -->
<p>The count is {count}</p>

<script lang="ts">
	import { getContext } from 'svelte';

	const count = getContext('count');
</script>

<!-- This will never update -->
<p>The count is {count}</p>

To fix this, reference the variable such that it is lazily evaluated. For the above example, this can be achieved by wrapping count in a function:

Parent

<script>
	import { setContext } from 'svelte';

	let count = $state(0);
	setContext('count', () => count);
</script>

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

<script lang="ts">
	import { setContext } from 'svelte';

	let count = $state(0);
	setContext('count', () => count);
</script>

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

Child

<script>
	import { getContext } from 'svelte';

	const count = getContext('count');
</script>

<!-- This will update -->
<p>The count is {count()}</p>

<script lang="ts">
	import { getContext } from 'svelte';

	const count = getContext('count');
</script>

<!-- This will update -->
<p>The count is {count()}</p>

For more info, see Passing state into functions.

store_rune_conflict

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

`<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

`this` should be an `{expression}`. Using a string attribute value will cause an error in future versions of Svelte

svelte_self_deprecated

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

See the note in the docs for more info.

unknown_code

`%code%` is not a recognised code

`%code%` is not a recognised code (did you mean `%suggestion%`?)

Edit this page on GitHub

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