Source: [https://objectcomputing.com/resources/publications/sett/july-2019-web-dev-simplified-with-svelte] Svelte can bind a child component prop to a variable in the parent component. This allows child components to change values of parent component variables.
For example, here is a parent component:
<script>
import Child from './Child.svelte';
let pValue = 1;
</script>
<div>pValue = {pValue}</div>
<Child bind:cValue={pValue} />And here is the child component:
<script>
export let cValue = '';
const double = () => (cValue *= 2);
</script>
<div>cValue = {cValue}</div>
<button on:click={double}>Double</button>When the button in the Child component is pressed, cValue is doubled, and that becomes the new value of pValue because it is bound to cValue.