How to use the @lumino/domutils.ElementExt.hitTest function in @lumino/domutils

// Bail if the mouse is not over the button.
      if (!ElementExt.hitTest(this.decrementNode, mouseX, mouseY)) {
        return;
      }

      // Emit the step requested signal.
      this._stepRequested.emit('decrement');

      // Finished.
      return;
    }

    // Handle an increment button repeat.
    if (part === 'increment') {
      // Bail if the mouse is not over the button.
      if (!ElementExt.hitTest(this.incrementNode, mouseX, mouseY)) {
        return;
      }

      // Emit the step requested signal.
      this._stepRequested.emit('increment');

      // Finished.
      return;
    }

    // Handle a track repeat.
    if (part === 'track') {
      // Bail if the mouse is not over the track.
      if (!ElementExt.hitTest(this.trackNode, mouseX, mouseY)) {
        return;
      }

// Bail if the thumb was pressed.
    if (part === 'thumb') {
      return;
    }

    // Schedule the timer for another repeat.
    this._repeatTimer = window.setTimeout(this._onRepeat, 20);

    // Get the current mouse position.
    let mouseX = this._pressData.mouseX;
    let mouseY = this._pressData.mouseY;

    // Handle a decrement button repeat.
    if (part === 'decrement') {
      // Bail if the mouse is not over the button.
      if (!ElementExt.hitTest(this.decrementNode, mouseX, mouseY)) {
        return;
      }

      // Emit the step requested signal.
      this._stepRequested.emit('decrement');

      // Finished.
      return;
    }

    // Handle an increment button repeat.
    if (part === 'increment') {
      // Bail if the mouse is not over the button.
      if (!ElementExt.hitTest(this.incrementNode, mouseX, mouseY)) {
        return;
      }

private _evtMouseLeave(event: MouseEvent): void {
    // Cancel any pending submenu opening.
    this._cancelOpenTimer();

    // If there is no open child menu, just reset the active index.
    if (!this._childMenu) {
      this.activeIndex = -1;
      return;
    }

    // If the mouse is over the child menu, cancel the close timer.
    let { clientX, clientY } = event;
    if (ElementExt.hitTest(this._childMenu.node, clientX, clientY)) {
      this._cancelCloseTimer();
      return;
    }

    // Otherwise, reset the active index and start the close timer.
    this.activeIndex = -1;
    this._startCloseTimer();
  }

private _evtMouseDown(event: MouseEvent): void {
    // Bail if the mouse press was not on the menu bar. This can occur
    // when the document listener is installed for an active menu bar.
    if (!ElementExt.hitTest(this.node, event.clientX, event.clientY)) {
      return;
    }

    // Stop the propagation of the event. Immediate propagation is
    // also stopped so that an open menu does not handle the event.
    event.preventDefault();
    event.stopPropagation();
    event.stopImmediatePropagation();

    // Check if the mouse is over one of the menu items.
    let index = ArrayExt.findFirstIndex(this.contentNode.children, node => {
      return ElementExt.hitTest(node, event.clientX, event.clientY);
    });

    // If the press was not on an item, close the child menu.
    if (index === -1) {

function findDropTarget(
    panel: DockPanel,
    clientX: number,
    clientY: number,
    edges: DockPanel.IEdges
  ): IDropTarget {
    // Bail if the mouse is not over the dock panel.
    if (!ElementExt.hitTest(panel.node, clientX, clientY)) {
      return { zone: 'invalid', target: null };
    }

    // Look up the layout for the panel.
    let layout = panel.layout as DockLayout;

    // If the layout is empty, indicate the entire root drop zone.
    if (layout.isEmpty) {
      return { zone: 'root-all', target: null };
    }

    // Test the edge zones when in multiple document mode.
    if (panel.mode === 'multiple-document') {
      // Get the client rect for the dock panel.
      let panelRect = panel.node.getBoundingClientRect();

let index = ArrayExt.findFirstIndex(this.contentNode.children, node => {
      return ElementExt.hitTest(node, event.clientX, event.clientY);
    });

let index = ArrayExt.findFirstIndex(tabs, tab => {
      return ElementExt.hitTest(tab, event.clientX, event.clientY);
    });

let index = ArrayExt.findFirstIndex(this.contentNode.children, node => {
      return ElementExt.hitTest(node, event.clientX, event.clientY);
    });

function hitTestMenus(menu: Menu, x: number, y: number): boolean {
    for (let temp: Menu | null = menu; temp; temp = temp.childMenu) {
      if (ElementExt.hitTest(temp.node, x, y)) {
        return true;
      }
    }
    return false;
  }

return ArrayExt.findFirstIndex(nodes, node => {
      return ElementExt.hitTest(node, x, y);
    });
  }