private _updateTabIndexes()

in packages/react-focus/src/components/FocusZone/FocusZone.tsx [1240:1308]
62 lines of code
33 McCabe index (conditional complexity)

  private _updateTabIndexes(element?: HTMLElement): void {
    if (
      !this._activeElement &&
      this.props.defaultTabbableElement &&
      typeof this.props.defaultTabbableElement === 'function'
    ) {
      this._activeElement = this.props.defaultTabbableElement(this._root.current as HTMLElement);
    }

    if (!element && this._root.current) {
      this._defaultFocusElement = null;
      element = this._root.current;
      if (this._activeElement && !elementContains(element, this._activeElement)) {
        this._activeElement = null;
      }
    }

    // If active element changes state to disabled, set it to null.
    // Otherwise, we lose keyboard accessibility to other elements in focus zone.
    if (this._activeElement && !isElementTabbable(this._activeElement)) {
      this._activeElement = null;
    }

    const childNodes = element && element.children;

    for (let childIndex = 0; childNodes && childIndex < childNodes.length; childIndex++) {
      const child = childNodes[childIndex] as HTMLElement;

      if (!isElementFocusZone(child)) {
        // If the item is explicitly set to not be focusable then TABINDEX needs to be set to -1.
        if (child.getAttribute && child.getAttribute(IS_FOCUSABLE_ATTRIBUTE) === 'false') {
          child.setAttribute(TABINDEX, '-1');
        }

        if (isElementTabbable(child)) {
          if (this.props.disabled) {
            child.setAttribute(TABINDEX, '-1');
          } else if (
            !this._isInnerZone &&
            ((!this._activeElement && !this._defaultFocusElement) || this._activeElement === child)
          ) {
            this._defaultFocusElement = child;
            if (child.getAttribute(TABINDEX) !== '0') {
              child.setAttribute(TABINDEX, '0');
            }
          } else if (child.getAttribute(TABINDEX) !== '-1') {
            child.setAttribute(TABINDEX, '-1');
          }
        } else if (child.tagName === 'svg' && child.getAttribute('focusable') !== 'false') {
          // Disgusting IE hack. Sad face.
          child.setAttribute('focusable', 'false');
        }
      } else if (child.getAttribute(IS_FOCUSABLE_ATTRIBUTE) === 'true') {
        if (
          !this._isInnerZone &&
          ((!this._activeElement && !this._defaultFocusElement) || this._activeElement === child)
        ) {
          this._defaultFocusElement = child;
          if (child.getAttribute(TABINDEX) !== '0') {
            child.setAttribute(TABINDEX, '0');
          }
        } else if (child.getAttribute(TABINDEX) !== '-1') {
          child.setAttribute(TABINDEX, '-1');
        }
      }

      this._updateTabIndexes(child);
    }
  }