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Every block-level element has clientWidth, clientHeight, offsetWidth and offsetHeight bindings:

App.svelte
<div bind:clientWidth={w} bind:clientHeight={h}>
	<span style="font-size: {size}px" contenteditable>{text}</span>
	<span class="size">{w} x {h}px</span>
</div>

These bindings are readonly — changing the values of w and h won't have any effect on the element.

Elements are measured using a technique similar to this one. There is some overhead involved, so it's not recommended to use this for large numbers of elements.

display: inline elements cannot be measured with this approach; nor can elements that can't contain other elements (such as <canvas>). In these cases you will need to measure a wrapper element instead.

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<script>
	let w;
	let h;
	let size = 42;
	let text = 'edit this text';
</script>
 
<label>
	<input type="range" bind:value={size} min="10" max="100" />
	font size ({size}px)
</label>
 
<div>
	<span style="font-size: {size}px" contenteditable>{text}</span>
	<span class="size">{w} x {h}px</span>
</div>
 
<style>
	div {
		position: relative;
		display: inline-block;
		padding: 0.5rem;
		background: hsla(15, 100%, 50%, 0.1);
		border: 1px solid hsl(15, 100%, 50%);
	}
 
	.size {
		position: absolute;
		right: -1px;
		bottom: -1.4em;
		line-height: 1;
		background: hsl(15, 100%, 50%);
		color: white;
		padding: 0.2em 0.5em;
		white-space: pre;
	}
</style>
 
initialising