code: function handleBackspace(element) {
    const length = element[typedPrefixKey] ? element[typedPrefixKey].length : 0;
    if (length > 0) {
      element[typedPrefixKey] = element[typedPrefixKey].substr(0, length - 1);
    }
    element.selectItemWithTextPrefix(element[typedPrefixKey]);
    setPrefixTimeout(element);
  }
docs: Handle the Backspace key: remove the last character from the prefix.