Object

Defines callbacks onFirst and/or onEmpty.

const keyTreeCallbacks = {
    onFirst: function() {

        // called when the first node is added
    },
    onEmpty: function() {

        // called when all nodes are removed
    }
};
const keyTree = new KeyTree( [ Object, Object, Array ], keyTreeCallbacks );

function handler1() {}

keyTree.add( [ "click", "li", handler1 ] );

// onFirst is called with a context (`this`) of the keyTree instance and no arguments

keyTree.delete( [] );

// onEmpty is called with a context (`this`) of the keyTree instance and no arguments