HTMLSlotElement: slotchange event

The slotchange event is fired on an HTMLSlotElement instance (<slot> element) when the node(s) contained in that slot change.

In order to trigger a slotchange event, one has to set or remove the slot attribute.

element.setAttribute('slot', slotName);
// element.assignedSlot = $slot
element.removeAttribute('slot');
// element.assignedSlot = null

The following snippet is taken from our slotchange example (see it live also).

let slots = this.shadowRoot.querySelectorAll('slot');
slots[1].addEventListener('slotchange', function(e) {
  let nodes = slots[1].assignedNodes();
  console.log('Element in Slot "' + slots[1].name + '" changed to "' + nodes[0].outerHTML + '".');
});

Here we grab references to all the <slot>s, then add a slotchange event listener to the template's second slot — which is the one which has its contents changed in the example.

Every time the element inserted in the slot changes, we log a report to the console saying which slot has changed, and what the new node inside the slot is.