trilium/apps/client/src/widgets/buttons/close_pane_button.tsx

import { useEffect, useState } from "preact/hooks";
import { t } from "../../services/i18n";
import ActionButton from "../react/ActionButton";
import { useNoteContext, useTriliumEvent } from "../react/hooks";

export default function ClosePaneButton() {
    const { noteContext, ntxId, parentComponent } = useNoteContext();
    const [ isEnabled, setIsEnabled ] = useState(false);

    function refresh() {
        setIsEnabled(!!(noteContext && !!noteContext.mainNtxId));
    }

    useTriliumEvent("noteContextReorder", refresh);
    useEffect(refresh, [ ntxId ]);

    return (
        <ActionButton
            icon="bx bx-x"
            text={t("close_pane_button.close_this_pane")}
            className={!isEnabled ? "hidden-ext" : ""}
            onClick={(e) => {
                // to avoid split pane container detecting click within the pane which would try to activate this
                // pane (which is being removed)
                e.stopPropagation();

                parentComponent?.triggerCommand("closeThisNoteSplit", { ntxId: parentComponent.getClosestNtxId() });
            }}
        />
    )
}