When Svelte runs an effect function, it tracks which pieces of state (and derived state) are accessed (unless accessed inside [`untrack`](svelte#untrack)), and re-runs the function when that state later changes.
When Svelte runs an effect function, it tracks which pieces of state (and derived state) are accessed (unless accessed inside [`untrack`](svelte#untrack)), and re-runs the function when that state later changes.
@ -135,19 +135,33 @@ An effect only reruns when the object it reads changes, not when a property insi
An effect only depends on the values that it read the last time it ran. This has interesting implications for effects that have conditional code.
An effect only depends on the values that it read the last time it ran. This has interesting implications for effects that have conditional code.
For instance, if `a` is `true` in the code snippet below, the code inside the `if` block will run and `b` will be evaluated. As such, changes to either `a` or `b` [will cause the effect to re-run](/playground/untitled#H4sIAAAAAAAAE3VQzWrDMAx-FdUU4kBp71li6EPstOxge0ox8-QQK2PD-N1nLy2F0Z2Evj9_chKkP1B04pnYscc3cRCT8xhF95IEf8-Vq0DBr8rzPB_jJ3qumNERH-E2ECNxiRF9tIubWY00lgcYNAywj6wZJS8rtk83wjwgCrXHaULLUrYwKEgVGrnkx-Dx6MNFNstK5OjSbFGbwE0gdXuT_zGYrjmAuco515Hr1p_uXak3K3MgCGS9s-9D2grU-judlQYXIencnzad-tdR79qZrMyvw9wd5Z8Yv1h09dz8mn8AkM7Pfo0BAAA=).
For instance, if `condition` is `true` in the code snippet below, the code inside the `if` block will run and `color` will be evaluated. As such, changes to either `condition` or `color` [will cause the effect to re-run](/playground/untitled#H4sIAAAAAAAAE21RQW6DMBD8ytaNBJHaJFLViwNIVZ8RcnBgXVk1xsILTYT4e20TQg89IOPZ2fHM7siMaJBx9tmaWpFqjQNlAKXEihx7YVJpdIyfRkY3G4gB8Pi97cPanRtQU8AuwuF_eNUaQuPlOMtc1SlLRWlKUo1tOwJflUikQHZtA0klzCDc64Imx0ANn8bInV1CDhtHgjClrsftcSXotluLybOUb3g4JJHhOZs5WZpuIS9gjNqkJKQP5e2ClrR4SMdZ13E4xZ8zTPOTJU2A2uE_PQ9COCI926_hTVarIU4hu_REPlBrKq2q73ycrf1N-vS4TMUsulaVg3EtR8H9rFgsg8uUsT1B2F9eshigZHBRpuaD0D3mY8Qm2BfB5N2YyRzdNEYVDy0Ja-WsFjcOUuP1HvFLWA6H3XuHTUSmmDV2--0TXonxsKbp7G9C6R__NONS-MFNvxj_d6mBAgAA).
Conversely, if `a` is `false`, `b` will not be evaluated, and the effect will _only_ re-run when `a` changes.
Conversely, if `condition` is `false`, `color` will not be evaluated, and the effect will _only_ re-run again when `condition` changes.
```ts
```ts
let a = false;
// @filename: ambient.d.ts
let b = false;
declare module 'canvas-confetti' {
interface ConfettiOptions {
colors: string[];
}
function confetti(opts?: ConfettiOptions): void;
export default confetti;
}
// @filename: index.js
// ---cut---
// ---cut---
$effect(() => {
import confetti from 'canvas-confetti';
console.log('running');
let condition = $state(true);
let color = $state('#ff3e00');
if (a) {
$effect(() => {
console.log('b:', b);
if (condition) {
confetti({ colors: [color] });
} else {
confetti();
}
}
});
});
```
```
@ -211,20 +225,19 @@ It is used to implement abstractions like [`createSubscriber`](/docs/svelte/svel
The `$effect.root` rune is an advanced feature that creates a non-tracked scope that doesn't auto-cleanup. This is useful for nested effects that you want to manually control. This rune also allows for the creation of effects outside of the component initialisation phase.
The `$effect.root` rune is an advanced feature that creates a non-tracked scope that doesn't auto-cleanup. This is useful for nested effects that you want to manually control. This rune also allows for the creation of effects outside of the component initialisation phase.
When compiling a component as a custom element, the `$host` rune provides access to the host element, allowing you to (for example) dispatch custom events ([demo](/playground/untitled#H4sIAAAAAAAAE41Ry2rDMBD8FSECtqkTt1fHFpSSL-ix7sFRNkTEXglrnTYY_3uRlDgxTaEHIfYxs7szA9-rBizPPwZOZwM89wmecqxbF70as7InaMjltrWFR3mpkQDJ8pwXVnbKkKiwItUa3RGLVtk7gTHQXRDR2lXda4CY1D0SK9nCUk0QPyfrCovsRoNFe17aQOAwGncgO2gBqRzihJXiQrEs2csYOhQ-7HgKHaLIbpRhhBG-I2eD_8ciM4KnnOCbeE5dD2P6h0Dz0-Yi_arNhPLJXBtSGi2TvSXdbpqwdsXvjuYsC1veabvvUTog2ylrapKH2G2XsMFLS4uDthQnq2t1cwKkGOGLvYU5PvaQxLsxOkPmsm97Io1Mo2yUPF6VnOZFkw1RMoopKLKAE_9gmGxyDFMwMcwN-Bx_ABXQWmOtAgAA)):
When compiling a component as a [custom element](custom-elements), the `$host` rune provides access to the host element, allowing you to (for example) dispatch custom events ([demo](/playground/untitled#H4sIAAAAAAAAE41Ry2rDMBD8FSECtqkTt1fHFpSSL-ix7sFRNkTEXglrnTYY_3uRlDgxTaEHIfYxs7szA9-rBizPPwZOZwM89wmecqxbF70as7InaMjltrWFR3mpkQDJ8pwXVnbKkKiwItUa3RGLVtk7gTHQXRDR2lXda4CY1D0SK9nCUk0QPyfrCovsRoNFe17aQOAwGncgO2gBqRzihJXiQrEs2csYOhQ-7HgKHaLIbpRhhBG-I2eD_8ciM4KnnOCbeE5dD2P6h0Dz0-Yi_arNhPLJXBtSGi2TvSXdbpqwdsXvjuYsC1veabvvUTog2ylrapKH2G2XsMFLS4uDthQnq2t1cwKkGOGLvYU5PvaQxLsxOkPmsm97Io1Mo2yUPF6VnOZFkw1RMoopKLKAE_9gmGxyDFMwMcwN-Bx_ABXQWmOtAgAA)):
@ -22,10 +22,6 @@ The `transition:` directive indicates a _bidirectional_ transition, which means
{/if}
{/if}
```
```
## Built-in transitions
A selection of built-in transitions can be imported from the [`svelte/transition`](svelte-transition) module.
## Local vs global
## Local vs global
Transitions are local by default. Local transitions only play when the block they belong to is created or destroyed, _not_ when parent blocks are created or destroyed.
Transitions are local by default. Local transitions only play when the block they belong to is created or destroyed, _not_ when parent blocks are created or destroyed.
@ -40,6 +36,10 @@ Transitions are local by default. Local transitions only play when the block the
{/if}
{/if}
```
```
## Built-in transitions
A selection of built-in transitions can be imported from the [`svelte/transition`](svelte-transition) module.
@ -161,7 +161,7 @@ Tried to unmount a component that was not mounted
### ownership_invalid_binding
### 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%
%parent% passed property `%prop%` to %child% with `bind:`, but its parent component %owner% did not declare `%prop%` as a binding. Consider creating a binding between %owner% and %parent% (e.g. `bind:%prop%={...}` instead of `%prop%={...}`)
```
```
Consider three components `GrandParent`, `Parent` and `Child`. If you do `<GrandParent bind:value>`, inside `GrandParent` pass on the variable via `<Parent {value} />` (note the missing `bind:`) and then do `<Child bind:value>` inside `Parent`, this warning is thrown.
Consider three components `GrandParent`, `Parent` and `Child`. If you do `<GrandParent bind:value>`, inside `GrandParent` pass on the variable via `<Parent {value} />` (note the missing `bind:`) and then do `<Child bind:value>` inside `Parent`, this warning is thrown.
@ -171,11 +171,7 @@ To fix it, `bind:` to the value instead of just passing a property (i.e. in this
### ownership_invalid_mutation
### 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
Mutating unbound props (`%name%`, at %location%) is strongly discouraged. Consider using `bind:%prop%={...}` in %parent% (or using 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
@ -132,7 +132,7 @@ During development, this error is often preceeded by a `console.error` detailing
## ownership_invalid_binding
## 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%
> %parent% passed property `%prop%` to %child% with `bind:`, but its parent component %owner% did not declare `%prop%` as a binding. Consider creating a binding between %owner% and %parent% (e.g. `bind:%prop%={...}` instead of `%prop%={...}`)
Consider three components `GrandParent`, `Parent` and `Child`. If you do `<GrandParent bind:value>`, inside `GrandParent` pass on the variable via `<Parent {value} />` (note the missing `bind:`) and then do `<Child bind:value>` inside `Parent`, this warning is thrown.
Consider three components `GrandParent`, `Parent` and `Child`. If you do `<GrandParent bind:value>`, inside `GrandParent` pass on the variable via `<Parent {value} />` (note the missing `bind:`) and then do `<Child bind:value>` inside `Parent`, this warning is thrown.
@ -140,9 +140,7 @@ To fix it, `bind:` to the value instead of just passing a property (i.e. in this
## ownership_invalid_mutation
## 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
> Mutating unbound props (`%name%`, at %location%) is strongly discouraged. Consider using `bind:%prop%={...}` in %parent% (or using 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
console.warn(`%c[svelte] ownership_invalid_binding\n%c${parent} passed a value to ${child} with \`bind:\`, but the value is owned by ${owner}. Consider creating a binding between ${owner} and ${parent}\nhttps://svelte.dev/e/ownership_invalid_binding`,bold,normal);
console.warn(`%c[svelte] ownership_invalid_binding\n%c${parent} passed property \`${prop}\` to ${child} with \`bind:\`, but its parent component ${owner} did not declare \`${prop}\` as a binding. Consider creating a binding between ${owner} and ${parent} (e.g. \`bind:${prop}={...}\` instead of \`${prop}={...}\`)\nhttps://svelte.dev/e/ownership_invalid_binding`,bold,normal);
console.warn(`%c[svelte] ownership_invalid_mutation\n%c${component?`${component} mutated a value owned by ${owner}. This is strongly discouraged. Consider passing values to child components with \`bind:\`, or use a callback instead`:'Mutating a value outside the component that created it is strongly discouraged. Consider passing values to child components with `bind:`, or use a callback instead'}\nhttps://svelte.dev/e/ownership_invalid_mutation`,bold,normal);
console.warn(`%c[svelte] ownership_invalid_mutation\n%cMutating unbound props (\`${name}\`, at ${location}) is strongly discouraged. Consider using \`bind:${prop}={...}\` in ${parent} (or using a callback) instead\nhttps://svelte.dev/e/ownership_invalid_mutation`,bold,normal);
'Counter.svelte mutated a value owned by main.svelte. This is strongly discouraged. Consider passing values to child components with `bind:`, or use a callback instead';
'Mutating unbound props (`object`, at Counter.svelte:5:23) is strongly discouraged. Consider using `bind:object={...}` in main.svelte (or using a callback) instead';
'Intermediate.svelte passed a value to Counter.svelte with `bind:`, but the value is owned by main.svelte. Consider creating a binding between main.svelte and Intermediate.svelte'
'Intermediate.svelte passed property `object` to Counter.svelte with `bind:`, but its parent component main.svelte did not declare `object` as a binding. Consider creating a binding between main.svelte and Intermediate.svelte (e.g. `bind:object={...}` instead of `object={...}`)'
'Counter.svelte mutated a value owned by main.svelte. This is strongly discouraged. Consider passing values to child components with `bind:`, or use a callback instead'
'Mutating unbound props (`notshared`, at Counter.svelte:10:23) is strongly discouraged. Consider using `bind:notshared={...}` in main.svelte (or using a callback) instead'
ComputerGuy
5 months ago