diff --git a/documentation/docs/03-runes/02-side-effects.md b/documentation/docs/03-runes/02-side-effects.md index 9cc0f15beb..f4bc8ef947 100644 --- a/documentation/docs/03-runes/02-side-effects.md +++ b/documentation/docs/03-runes/02-side-effects.md @@ -122,6 +122,21 @@ An effect only reruns when the object it reads changes, not when a property insi

{state.value} doubled is {derived.value}

``` +An effect only depends on the values that it read the last time it ran. If `a` is true, changes to `b` will [not cause this effect to rerun](/#H4sIAAAAAAAAE3WQ0WrDMAxFf0U1hTow1vcsMfQ7lj3YjlxEXTvEymC4_vfFC6Ewtidxde8RkrJw5DGJ9j2LoO8oWnGZJvEi-GuqIn2iZ1x1istsa6dLdqaJ1RAG9sigoYdjYs0onfYJm7fdMX85q3dE59CylA30CnJtDWxjSNHjq49XeZqXEChcT9usLUAOpIbHA0yzM78oColGhDVofLS3neZSS6mqOz-XD51ZmGOAGKwne-vztk-956CL0kAJsi7decupf4l658EUZX4I8yTWt93jSI5wFC3PC5aP8g0Aje5DcQEAAA==): + +```ts +let a = false; +let b = false; +// ---cut--- +$effect(() => { + console.log('running'); + + if (a || b) { + console.log('inside if block'); + } +}); +``` + ## When not to use `$effect` In general, `$effect` is best considered something of an escape hatch — useful for things like analytics and direct DOM manipulation — rather than a tool you should use frequently. In particular, avoid using it to synchronise state. Instead of this... diff --git a/sites/svelte-5-preview/src/routes/docs/content/01-api/02-runes.md b/sites/svelte-5-preview/src/routes/docs/content/01-api/02-runes.md index 02cea6ffb4..84062a1cfa 100644 --- a/sites/svelte-5-preview/src/routes/docs/content/01-api/02-runes.md +++ b/sites/svelte-5-preview/src/routes/docs/content/01-api/02-runes.md @@ -258,6 +258,21 @@ An effect only reruns when the object it reads changes, not when a property insi

{state.value} doubled is {derived.value}

``` +An effect only depends on the values that it read the last time it ran. If `a` is true, changes to `b` will [not cause this effect to rerun](/#H4sIAAAAAAAAE3WQ0WrDMAxFf0U1hTow1vcsMfQ7lj3YjlxEXTvEymC4_vfFC6Ewtidxde8RkrJw5DGJ9j2LoO8oWnGZJvEi-GuqIn2iZ1x1istsa6dLdqaJ1RAG9sigoYdjYs0onfYJm7fdMX85q3dE59CylA30CnJtDWxjSNHjq49XeZqXEChcT9usLUAOpIbHA0yzM78oColGhDVofLS3neZSS6mqOz-XD51ZmGOAGKwne-vztk-956CL0kAJsi7decupf4l658EUZX4I8yTWt93jSI5wFC3PC5aP8g0Aje5DcQEAAA==): + +```ts +let a = false; +let b = false; +// ---cut--- +$effect(() => { + console.log('running'); + + if (a || b) { + console.log('inside if block'); + } +}); +``` + You can return a function from `$effect`, which will run immediately before the effect re-runs, and before it is destroyed ([demo](/#H4sIAAAAAAAAE42SzW6DMBCEX2Vl5RDaVCQ9JoDUY--9lUox9lKsGBvZC1GEePcaKPnpqSe86_m0M2t6ViqNnu0_e2Z4jWzP3pqGbRhdmrHwHWrCUHvbOjF2Ei-caijLTU4aCYRtDUEKK0-ccL2NDstNrbRWHoU10t8Eu-121gTVCssSBa3XEaQZ9GMrpziGj0p5OAccCgSHwmEgJZwrNNihg6MyhK7j-gii4uYb_YyGUZ5guQwzPdL7b_U4ZNSOvp9T2B3m1rB5cLx4zMkhtc7AHz7YVCVwEFzrgosTBMuNs52SKDegaPbvWnMH8AhUXaNUIY6-hHCldQhUIcyLCFlfAuHvkCKaYk8iYevGGgy2wyyJnpy9oLwG0sjdNe2yhGhJN32HsUzi2xOapNpl_bSLIYnDeeoVLZE1YI3QSpzSfo7-8J5PKbwOmdf2jC6JZyD7HxpPaMk93aHhF6utVKVCyfbkWhy-hh9Z3o_2nQIAAA==)). ```svelte