How to use the slate-hotkeys.isCompose function in slate-hotkeys

function onKeyDown(event, editor, next) {
    if (editor.readOnly) return

    // When composing, we need to prevent all hotkeys from executing while
    // typing. However, certain characters also move the selection before
    // we're able to handle it, so prevent their default behavior.
    if (isComposing) {
      if (Hotkeys.isCompose(event)) event.preventDefault()
      return
    }

    // Certain hotkeys have native editing behaviors in `contenteditable`
    // elements which will editor the DOM and cause our value to be out of sync,
    // so they need to always be prevented.
    if (
      !IS_IOS &&
      (Hotkeys.isBold(event) ||
        Hotkeys.isDeleteBackward(event) ||
        Hotkeys.isDeleteForward(event) ||
        Hotkeys.isDeleteLineBackward(event) ||
        Hotkeys.isDeleteLineForward(event) ||
        Hotkeys.isDeleteWordBackward(event) ||
        Hotkeys.isDeleteWordForward(event) ||
        Hotkeys.isItalic(event) ||