mirror of https://github.com/sveltejs/svelte
22 lines
568 B
22 lines
568 B
---
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title: Assignments
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---
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At the heart of Svelte is a powerful system of _reactivity_ for keeping the DOM in sync with your application state — for example, in response to an event.
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To demonstrate it, we first need to wire up an event handler. Replace line 9 with this:
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```svelte
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<button on:click={incrementCount}>
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```
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Inside the `incrementCount` function, all we need to do is change the value of `count`:
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```js
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function incrementCount() {
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count += 1;
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}
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```
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Svelte 'instruments' this assignment with some code that tells it the DOM will need to be updated.
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