6.0 KiB
assignment_value_stale
Assignment to `%property%` property (%location%) will evaluate to the right-hand side, not the value of `%property%` following the assignment. This may result in unexpected behaviour.
Given a case like this...
<script>
let object = $state({ array: null });
function add() {
(object.array ??= []).push(object.array.length);
}
</script>
<button onclick={add}>add</button>
<p>items: {JSON.stringify(object.items)}</p>
...the array being pushed to when the button is first clicked is the [] on the right-hand side of the assignment, but the resulting value of object.array is an empty state proxy. As a result, the pushed value will be discarded.
You can fix this by separating it into two statements:
let object = { array: [0] };
// ---cut---
function add() {
object.array ??= [];
object.array.push(object.array.length);
}
binding_property_non_reactive
`%binding%` is binding to a non-reactive property
`%binding%` (%location%) is binding to a non-reactive property
console_log_state
Your `console.%method%` contained `$state` proxies. Consider using `$inspect(...)` or `$state.snapshot(...)` instead
When logging a proxy, browser devtools will log the proxy itself rather than the value it represents. In the case of Svelte, the 'target' of a $state proxy might not resemble its current value, which can be confusing.
The easiest way to log a value as it changes over time is to use the $inspect rune. Alternatively, to log things on a one-off basis (for example, inside an event handler) you can use $state.snapshot to take a snapshot of the current value.
event_handler_invalid
%handler% should be a function. Did you mean to %suggestion%?
hydration_attribute_changed
The `%attribute%` attribute on `%html%` changed its value between server and client renders. The client value, `%value%`, will be ignored in favour of the server value
hydration_html_changed
The value of an `{@html ...}` block changed between server and client renders. The client value will be ignored in favour of the server value
The value of an `{@html ...}` block %location% changed between server and client renders. The client value will be ignored in favour of the server value
hydration_mismatch
Hydration failed because the initial UI does not match what was rendered on the server
Hydration failed because the initial UI does not match what was rendered on the server. The error occurred near %location%
invalid_raw_snippet_render
The `render` function passed to `createRawSnippet` should return HTML for a single element
legacy_recursive_reactive_block
Detected a migrated `$:` reactive block in `%filename%` that both accesses and updates the same reactive value. This may cause recursive updates when converted to an `$effect`.
lifecycle_double_unmount
Tried to unmount a component that was not mounted
ownership_invalid_binding
%parent% passed a value to %child% with `bind:`, but the value is owned by %owner%. Consider creating a binding between %owner% and %parent%
ownership_invalid_mutation
Mutating a value outside the component that created it is strongly discouraged. Consider passing values to child components with `bind:`, or use a callback instead
%component% mutated a value owned by %owner%. This is strongly discouraged. Consider passing values to child components with `bind:`, or use a callback instead
reactive_declaration_non_reactive_property
A `$:` statement (%location%) read reactive state that was not visible to the compiler. Updates to this state will not cause the statement to re-run. The behaviour of this code will change if you migrate it to runes mode
In legacy mode, a $: reactive statement re-runs when the state it references changes. This is determined at compile time, by analysing the code.
In runes mode, effects and deriveds re-run when there are changes to the values that are read during the function's execution.
Often, the result is the same — for example these can be considered equivalent:
let a = 1, b = 2, sum = 3;
// ---cut---
$: sum = a + b;
let a = 1, b = 2;
// ---cut---
const sum = $derived(a + b);
In some cases — such as the one that triggered the above warning — they are not the same:
let a = 1, b = 2, sum = 3;
// ---cut---
const add = () => a + b;
// the compiler can't 'see' that `sum` depends on `a` and `b`, but
// they _would_ be read while executing the `$derived` version
$: sum = add();
Similarly, reactive properties of deep state are not visible to the compiler. As such, changes to these properties will cause effects and deriveds to re-run but will not cause $: statements to re-run.
When you migrate this component to runes mode, the behaviour will change accordingly.
state_proxy_equality_mismatch
Reactive `$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.