Svelte基础
Advanced Svelte
Advanced reactivity
Motion
Advanced bindings
Advanced transitions
Context API
Special elements
<script module>
Next steps
Basic SvelteKit
Introduction
Routing
Loading data
Headers and cookies
Shared modules
API routes
$app/state
Errors and redirects
Advanced SvelteKit
Page options
Link options
Advanced routing
Advanced loading
Environment variables
Conclusion
You can use the special bind:this directive to get a readonly binding to an element in your component.
The $effect in this exercise attempts to create a canvas context, but canvas is undefined. Begin by declaring it at the top level of the component...
App
<script>
import { paint } from './gradient.js';
let canvas;
$effect(() => {
// ...
});
</script><script lang="ts">
import { paint } from './gradient.js';
let canvas;
$effect(() => {
// ...
});
</script>...then add the directive to the <canvas> element:
App
<canvas bind:this={canvas} width={32} height={32}></canvas>Note that the value of canvas will remain undefined until the component has mounted — in other words you can’t access it until the $effect runs.
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<script>
import { paint } from './gradient.js'; $effect(() => { const context = canvas.getContext('2d'); let frame = requestAnimationFrame(function loop(t) {frame = requestAnimationFrame(loop);
paint(context, t);
});
return () => {cancelAnimationFrame(frame);
};
});
</script>
<canvas width={32} height={32}></canvas><style>
canvas {position: fixed;
left: 0;
top: 0;
width: 100%;
height: 100%;
background-color: #666;
mask: url(./svelte-logo-mask.svg) 50% 50% no-repeat;
mask-size: 60vmin;
-webkit-mask: url(./svelte-logo-mask.svg) 50% 50% no-repeat;
-webkit-mask-size: 60vmin;
}
</style>