+
+ {count} doubled is {doubled}
-``` - -The expression inside `$derived(...)` should be free of side-effects. Svelte will disallow state changes (e.g. `count++`) inside derived expressions. - -As with `$state`, you can mark class fields as `$derived`. - -> [!LEGACY] -> In Svelte 4, you could use reactive statements for this. -> -> ```svelte -> -> -> -> ->{count} doubled is {doubled}
-> ``` -> -> This only worked at the top level of a component. - -## `$effect` - -To run _side-effects_ when the component is mounted to the DOM, and when values change, we can use the `$effect` rune ([demo](/playground/untitled#H4sIAAAAAAAAE31T24rbMBD9lUG7kAQ2sbdlX7xOYNk_aB_rQhRpbAsU2UiTW0P-vbrYubSlYGzmzMzROTPymdVKo2PFjzMzfIusYB99z14YnfoQuD1qQh-7bmdFQEonrOppVZmKNBI49QthCc-OOOH0LZ-9jxnR6c7eUpOnuv6KeT5JFdcqbvbcBcgDz1jXKGg6ncFyBedYR6IzLrAZwiN5vtSxaJA-EzadfJEjKw11C6GR22-BLH8B_wxdByWpvUYtqqal2XB6RVkG1CoHB6U1WJzbnYFDiwb3aGEdDa3Bm1oH12sQLTcNPp7r56m_00mHocSG97_zd7ICUXonA5fwKbPbkE2ZtMJGGVkEdctzQi4QzSwr9prnFYNk5hpmqVuqPQjNnfOJoMF22lUsrq_UfIN6lfSVyvQ7grB3X2mjMZYO3XO9w-U5iLx42qg29md3BP_ni5P4gy9ikTBlHxjLzAtPDlyYZmRdjAbGq7HprEQ7p64v4LU_guu0kvAkhBim3nMplWl8FreQD-CW20aZR0wq12t-KqDWeBywhvexKC3memmDwlHAv9q4Vo2ZK8KtK0CgX7u9J8wXbzdKv-nRnfF_2baTqlYoWUF2h5efl9-n0O6koAMAAA==)): - -```svelte - - - -``` - -The function passed to `$effect` will run when the component mounts, and will re-run after any changes to the values it reads that were declared with `$state` or `$derived` (including those passed in with `$props`). Re-runs are batched (i.e. changing `color` and `size` in the same moment won't cause two separate runs), and happen after any DOM updates have been applied. - -> [!LEGACY] -> In Svelte 4, you could use reactive statements for this. -> -> ```svelte -> -> -> -> ``` -> -> This only worked at the top level of a component. diff --git a/documentation/docs/02-runes/01-what-are-runes.md b/documentation/docs/02-runes/01-what-are-runes.md index dc163ebdf1..59c371eb49 100644 --- a/documentation/docs/02-runes/01-what-are-runes.md +++ b/documentation/docs/02-runes/01-what-are-runes.md @@ -2,7 +2,7 @@ title: What are runes? --- -> [!NOTE] **rune** /ro͞on/ _noun_ +> [!NOTE] **rune** /ruːn/ _noun_ > > A letter or mark used as a mystical or magic symbol. diff --git a/documentation/docs/02-runes/02-$state.md b/documentation/docs/02-runes/02-$state.md index 49e17cd08f..16630a977b 100644 --- a/documentation/docs/02-runes/02-$state.md +++ b/documentation/docs/02-runes/02-$state.md @@ -250,3 +250,83 @@ console.log(total.value); // 7 ``` ...though if you find yourself writing code like that, consider using [classes](#Classes) instead. + +## Passing state across modules + +You can declare state in `.svelte.js` and `.svelte.ts` files, but you can only _export_ that state if it's not directly reassigned. In other words you can't do this: + +```js +/// file: state.svelte.js +export let count = $state(0); + +export function increment() { + count += 1; +} +``` + +That's because every reference to `count` is transformed by the Svelte compiler — the code above is roughly equivalent to this: + +```js +/// file: state.svelte.js (compiler output) +// @filename: index.ts +interface Signal