Function cssFallback

packages/injected/src/selectorGenerator.ts:391–461

(injectedScript: InjectedScript, targetElement: Element, options: InternalOptions)

}

function cssFallback(injectedScript: InjectedScript, targetElement: Element, options: InternalOptions): SelectorToken[] {
  const root: Node = options.root ?? targetElement.ownerDocument;
  const tokens: string[] = [];

  function uniqueCSSSelector(prefix?: string): string | undefined {
    const path = tokens.slice();
    if (prefix)
      path.unshift(prefix);
    const selector = path.join(' > ');
    const parsedSelector = injectedScript.parseSelector(selector);
    const node = injectedScript.querySelector(parsedSelector, root, false);
    return node === targetElement ? selector : undefined;
  }

  function makeStrict(selector: string): SelectorToken[] {
    const token = { engine: 'css', selector, score: kCSSFallbackScore };
    const parsedSelector = injectedScript.parseSelector(selector);
    const elements = injectedScript.querySelectorAll(parsedSelector, root);
    if (elements.length === 1)
      return [token];
    const nth = { engine: 'nth', selector: String(elements.indexOf(targetElement)), score: kNthScore };
    return [token, nth];
  }

  for (let element: Element | undefined = targetElement; element && element !== root; element = parentElementOrShadowHost(element)) {
    let bestTokenForLevel: string = '';

    // Element ID is the strongest signal, use it.
    if (element.id && !options.noCSSId) {
      const token = makeSelectorForId(element.id);
      const selector = uniqueCSSSelector(token);
      if (selector)
        return makeStrict(selector);
      bestTokenForLevel = token;
    }

    const parent = element.parentNode as (Element | ShadowRoot);

    // Combine class names until unique.
    const classes = [...element.classList].map(escapeClassName);
    for (let i = 0; i < classes.length; ++i) {
      const token = '.' + classes.slice(0, i + 1).join('.');
      const selector = uniqueCSSSelector(token);
      if (selector)
        return makeStrict(selector);
      // Even if not unique, does this subset of classes uniquely identify node as a child?
      if (!bestTokenForLevel && parent) {
        const sameClassSiblings = parent.querySelectorAll(token);
        if (sameClassSiblings.length === 1)
          bestTokenForLevel = token;
      }
    }

    // Ordinal is the weakest signal.
    if (parent) {
      const siblings = [...parent.children];
      const nodeName = element.nodeName;
      const sameTagSiblings = siblings.filter(sibling => sibling.nodeName === nodeName);