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Part 1 / Logic / Each blocks

When building user interfaces you'll often find yourself working with lists of data. In this exercise, we've repeated the <button> markup multiple times — changing the colour each time — but there's still more to add.

Instead of laboriously copying, pasting and editing, we can get rid of all but the first button, then use an each block:

App.svelte
<div>
	{#each colors as color}
		<button
			aria-current="{selected === 'red' ? 'true' : undefined}"
			aria-label="red"
			style="background: red"
			on:click={() => selected = 'red'}
		></button>
	{/each}
</div>

The expression (colors, in this case) can be any array or array-like object (i.e. it has a length property). You can loop over generic iterables with each [...iterable].

Now we need to use the color variable in place of "red":

App.svelte
<div>
	{#each colors as color}
		<button
			aria-current="{selected === color ? 'true' : undefined}"
			aria-label={color}
			style="background: {color}"
			on:click={() => selected = color}
		></button>
	{/each}
</div>

You can get the current index as a second argument, like so:

App.svelte
<div>
	{#each colors as color, i}
		<button
			aria-current="{selected === color ? 'true' : undefined}"
			aria-label={color}
			style="background: {color}"
			on:click={() => selected = color}
		>{i + 1}</button>
	{/each}
</div>

Next: Keyed each blocks

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<script>
	const colors = ['red', 'orange', 'yellow', 'green', 'blue', 'indigo', 'violet'];
	let selected = colors[0];
</script>
 
<h1 style="color: {selected}">Pick a colour</h1>
 
<div>
	<button
		aria-current={selected === 'red'}
		aria-label="red"
		style="background: red"
		on:click={() => selected = 'red'}
	></button>
 
	<button
		aria-current={selected === 'orange'}
		aria-label="orange"
		style="background: orange"
		on:click={() => selected = 'orange'}
	></button>
 
	<button
		aria-current={selected === 'yellow'}
		aria-label="yellow"
		style="background: yellow"
		on:click={() => selected = 'yellow'}
	></button>
 
	<!-- TODO add the rest of the colours -->
	<button></button>
	<button></button>
	<button></button>
	<button></button>
</div>
 
<style>
	h1 {
		transition: color 0.2s;
	}
 
	div {
		display: grid;
		grid-template-columns: repeat(7, 1fr);
		grid-gap: 5px;
		max-width: 400px;
	}
 
	button {
		aspect-ratio: 1;
		border-radius: 50%;
		background: var(--color, #fff);
		transform: translate(-2px,-2px);
		filter: drop-shadow(2px 2px 3px rgba(0,0,0,0.2));
		transition: all 0.1s;
	}
 
	button[aria-current="true"] {
		transform: none;
		filter: none;
		box-shadow: inset 3px 3px 4px rgba(0,0,0,0.2);
	}
</style>
initialising