In a previous exercise, we learned how to use the onMount lifecycle function to paint to a canvas.
But the example is buggy — it's using document.querySelector('canvas'), which will always return the first <canvas> found on the page, which might not be the one belonging to our component.
Instead, we can use the readonly this binding to get a reference to the element:
App.svelte
let canvas;
onMount(() => {
const canvas = document.querySelector('canvas')
const context = canvas.getContext('2d');
let frame = requestAnimationFrame(function loop(t) {
frame = requestAnimationFrame(loop);
paint(context, t);
});
return () => {
cancelAnimationFrame(frame);
};
});App.svelte
<canvas
bind:this={canvas}
width={32}
height={32}
></canvas>Note that the value of canvas will be undefined until the component has mounted.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
<script>
import { onMount } from 'svelte'; import { paint } from './gradient.js'; onMount(() => { const canvas = document.querySelector('canvas') 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}/>
<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>