mirror of https://github.com/sveltejs/svelte
26 lines
628 B
26 lines
628 B
---
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title: The class directive
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---
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Like any other attribute, you can specify classes with a JavaScript attribute, seen here:
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<!-- prettier-ignore -->
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```svelte
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<button
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class={current === 'foo' ? 'selected' : ''}
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on:click={() => current = 'foo'}
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>foo</button>
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```
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This is such a common pattern in UI development that Svelte includes a special directive to simplify it:
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<!-- prettier-ignore -->
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```svelte
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<button
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class:selected={current === 'foo'}
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on:click={() => current = 'foo'}
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>foo</button>
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```
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The `selected` class is added to the element whenever the value of the expression is truthy, and removed when it's falsy.
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