Skip to main content

Just as you can bind to DOM elements, you can bind to component instances themselves with bind:this.

This is useful in the rare cases that you need to interact with a component programmatically (rather than by providing it with updated props). Revisiting our canvas app from a few exercises ago, it would be nice to add a button to clear the screen.

First, let's export a function from Canvas.svelte:

Canvas.svelte
export let color;
export let size;

export function clear() {
	context.clearRect(0, 0, canvas.width, canvas.height);
}

Then, create a reference to the component instance:

App.svelte
<script>
	import Canvas from './Canvas.svelte';
	import { trapFocus } from './actions.js';

	const colors = ['red', 'orange', 'yellow', 'green', 'blue', 'indigo', 'violet', 'white', 'black'];
	let selected = colors[0];
	let size = 10;

	let showMenu = true;
	let canvas;
</script>

<div class="container">
	<Canvas bind:this={canvas} color={selected} size={size} />

Finally, add a button that calls the clear function:

App.svelte
<div class="controls">
	<button class="show-menu" on:click={() => showMenu = !showMenu}>
		{showMenu ? 'close' : 'menu'}
	</button>

	<button on:click={() => canvas.clear()}>
		clear
	</button>
</div>

Next: Classes and styles

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
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
<script>
	import Canvas from './Canvas.svelte';
	import { trapFocus } from './actions.js';
 
	const colors = ['red', 'orange', 'yellow', 'green', 'blue', 'indigo', 'violet', 'white', 'black'];
	let selected = colors[0];
	let size = 10;
 
	let showMenu = true;
</script>
 
<div class="container">
	<Canvas color={selected} size={size} />
 
	{#if showMenu}
		<div
			class="modal-background"
			on:click|self={() => showMenu = false}
			on:keydown={(e) => {
				if (e.key === 'Escape') showMenu = false;
			}}
		>
			<div class="menu" use:trapFocus>
				<div class="colors">
					{#each colors as color}
						<button
							class="color"
							aria-label={color}
							aria-current={selected === color}
							style="--color: {color}"
							on:click={() => {
								selected = color;
							}}
						></button>
					{/each}
				</div>
 
				<label>
					small
					<input type="range" bind:value={size} min="1" max="50" />
					large
				</label>
			</div>
		</div>
	{/if}
 
	<div class="controls">
		<button class="show-menu" on:click={() => showMenu = !showMenu}>
			{showMenu ? 'close' : 'menu'}
		</button>
	</div>
</div>
 
<style>
	.container {
		position: fixed;
		left: 0;
		top: 0;
		width: 100%;
		height: 100%;
	}
 
	.controls {
		position: absolute;
		left: 0;
		top: 0;
		padding: 1em;
	}
 
	.show-menu {
		width: 5em;
	}
 
	.modal-background {
		position: fixed;
		display: flex;
		justify-content: center;
		align-items: center;
		left: 0;
		top: 0;
		width: 100%;
		height: 100%;
		backdrop-filter: blur(20px);
	}
 
	.menu {
		position: relative;
		background: var(--bg-2);
		width: calc(100% - 2em);
		max-width: 28em;
		padding: 1em 1em 0.5em 1em;
		border-radius: 1em;
		box-sizing: border-box;
		user-select: none;
	}
 
	.colors {
		display: grid;
		align-items: center;
		grid-template-columns: repeat(9, 1fr);
		grid-gap: 0.5em;
	}
 
	.color {
		aspect-ratio: 1;
		border-radius: 50%;
		background: var(--color, #fff);
		transform: none;
		filter: drop-shadow(2px 2px 3px rgba(0,0,0,0.2));
		transition: all 0.1s;
	}
 
	.color[aria-current="true"] {
		transform: translate(1px, 1px);
		filter: none;
		box-shadow: inset 3px 3px 4px rgba(0,0,0,0.2);
	}
 
	.menu label {
		display: flex;
		width: 100%;
		margin: 1em 0 0 0;
	}
 
	.menu input {
		flex: 1;
	}
</style>
initialising