clickOutside.ts

function clickOutside(node, handler) {
  function handleClick(event) {
    if (node && !node.contains(event.target) && !event.defaultPrevented) {
      handler()
    }
  }

  document.addEventListener('click', handleClick, true)

  return {
    destroy() {
      document.removeEventListener('click', handleClick, true)
    }
  }
}

export default clickOutside

Usage.svelte

<script type="ts">
    import onClickOutside from '../clickOutside'
</script>

<div use:onClickOutside={() => console.log('click')}>
  modal
</div>