HTMLSlotElement: assign() method

Baseline 2023

Newly available

Since March 2023, this feature works across the latest devices and browser versions. This feature might not work in older devices or browsers.

The assign() method of the HTMLSlotElement interface sets the slot's manually assigned nodes to an ordered set of slottables. The manually assigned nodes set is initially empty until nodes are assigned using assign().

Note: You cannot mix manually (imperative) and named (declarative, automatic) slot assignments. Therefore, for this method to work, the shadow tree needs to have been created with the slotAssignment: "manual" option.

Syntax

assign(node1)
assign(node1, node2)
assign(node1, node2, /* …, */ nodeN)

Parameters

node1, …, nodeN: A set of Element or Text nodes.

Return value

None (undefined).

Exceptions

NotAllowedError DOMException: Thrown when calling this method on an automatically assigned slot.

Examples

In the example below, the assign() method is used to display the correct tab in a tabbed application. The function is called and passed the panel to show, which is then assigned to the slot.

function UpdateDisplayTab(elem, tabIdx) {
  const shadow = elem.shadowRoot;
  const slot = shadow.querySelector("slot");
  const panels = elem.querySelectorAll("tab-panel");
  if (panels.length && tabIdx && tabIdx <= panels.length) {
    slot.assign(panels[tabIdx - 1]);
  } else {
    slot.assign();
  }
}

Specifications

Specification
HTML # dom-slot-assign