useCallback

// This function (component) is executed on every render
function Component() {
    // this event handler is redefined on every render
    const handleClick = () => alert("hello")

    // because `handleClick` is redefined on every render, `ChildComponent` will be re-rendered too. Because its `onClick` prop is considered changed.
    return <ChildComponent onClick={handleClick} />
}

<script>
    // In Svelte this isn't needed, because event handlers are declared inside <script> tags.
    // They aren't defined in the render path and therefore aren't redefined on every render.
    // They are defined once per component, so they work similar to how event handlers worked with React.Component.
</script>