You can not select more than 25 topics Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
svelte/site/content/tutorial/04-logic/05-keyed-each-blocks/text.md

20 lines
1.0 KiB

---
title: Keyed each blocks
---
By default, when you modify the value of an `each` block, it will add and remove items at the *end* of the block, and update any values that have changed. That might not be what you want.
It's easier to show why than to explain. Click the 'Remove first thing' button a few times, and notice that it's removing `<Thing>` components from the end and updating the `value` for those that remain. Instead, we'd like to remove the first `<Thing>` component and leave the rest unaffected.
To do that, we specify a unique identifier for the `each` block:
```html
{#each things as thing (thing.id)}
<Thing value={thing.value}/>
{/each}
```
The `(thing.id)` tells Svelte how to figure out what changed.
> You can use any object as the key, as Svelte uses a `Map` internally — in other words you could do `(thing)` instead of `(thing.id)`. Using a string or number is generally safer, however, since it means identity persists without referential equality, for example when updating with fresh data from an API server.