Part 3 / Advanced bindings / This
The readonly this binding applies to every element (and component) and allows you to obtain a reference to rendered elements. For example, we can get a reference to a <canvas> element:
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, so we put the logic inside the onMount lifecycle function.
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<script>
import { onMount } from 'svelte';let canvas;
onMount(() => { const ctx = canvas.getContext('2d');let frame = requestAnimationFrame(loop);
function loop(t) {frame = requestAnimationFrame(loop);
const imageData = ctx.getImageData(
0,
0,
canvas.width,
canvas.height
);
for (
let p = 0;
p < imageData.data.length;
p += 4
) {const i = p / 4;
const x = i % canvas.width;
const y = (i / canvas.width) >>> 0;
const r =
64 +
(128 * x) / canvas.width +
64 * Math.sin(t / 1000);
const g =
64 +
(128 * y) / canvas.height +
64 * Math.cos(t / 1000);
const b = 128;
imageData.data[p + 0] = r;
imageData.data[p + 1] = g;
imageData.data[p + 2] = b;
imageData.data[p + 3] = 255;
}
ctx.putImageData(imageData, 0, 0);
}
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: 40%;
-webkit-mask: url(svelte-logo-mask.svg) 50% 50% no-repeat;
-webkit-mask-size: 40%;
}
</style>
initialising