svelte/packages/svelte/messages/client-warnings/warnings.md

binding_property_non_reactive

%binding% is binding to a non-reactive property

%binding% (%location%) is binding to a non-reactive property

custom_element_invalid_attribute

<%name%> has a %prop% property, but it is specified as an attribute. Use %prop%={...}, without surrounding quotes, to treat it as a property instead

<%name%> (%location%) has a %prop% property, but is specified as an attribute. Use %prop%={...}, without surrounding quotes, to treat it as a property instead

When specifying attributes and properties on custom elements, values that are quoted are treated as attributes. Unquoted values are treated as properties.

custom_element_invalid_property

<%name%> does not have a %prop% property. Use %prop%="...", with the surrounding quotes, to treat it as an attribute instead

<%name%> (%location%) does not have a %prop% property. Use %prop%="...", with the surrounding quotes, to treat it as an attribute instead

event_handler_invalid

%handler% should be a function. Did you mean to %suggestion%?

hydration_attribute_changed

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

The value of an {@html ...} block changed between server and client renders. The client value will be ignored in favour of the server value

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

Hydration failed because the initial UI does not match what was rendered on the server

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

invalid_raw_snippet_render

The render function passed to createRawSnippet should return HTML for a single element

lifecycle_double_unmount

Tried to unmount a component that was not mounted

ownership_invalid_binding

%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

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

%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

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 of the value it is passed. The proxy and the value have different identities, meaning equality checks will always return false:

<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.