Reactive $: statements

<script>
	let a = 1;
	let b = 2;

	// this is a 'reactive statement', and it will re-run
	// when `a`, `b` or `sum` change
	$: console.log(`${a} + ${b} = ${sum}`);

	// this is a 'reactive assignment' — `sum` will be
	// recalculated when `a` or `b` change. It is
	// not necessary to declare `sum` separately
	$: sum = a + b;
</script>

$: {
	// recalculate `total` when `items` changes
	total = 0;

	for (const const item: anyitem of items) {
		total += const item: anyitem.value;
	}
}

$: ({ larry: anylarry, moe: anymoe, curly: anycurly } = stooges);

let let count: numbercount = 0;
let let double: () => numberdouble = () => let count: numbercount * 2;

$: doubled = let double: () => numberdouble();

<script>
	let x = 0;
	let y = 0;

	$: z = y;
	$: setY(x);

	function setY(value) {
		y = value;
	}
</script>

$: if (browser) {
	var document: Document
window.document returns a reference to the document contained in the window.
MDN Reference
document.Document.title: string
The document.title property gets or sets the current title of the document. When present, it defaults to the value of the