function getValueForAttribute(node, name, expected, isCustomComponentTag) {
    {
      if (!isAttributeNameSafe(name)) {
        return;
      }

      if (!node.hasAttribute(name)) {
        return expected === undefined ? undefined : null;
      }

      var value = node.getAttribute(name);

      {
        checkAttributeStringCoercion(expected, name);
      }

      if (value === '' + expected) {
        return expected;
      }

      return value;
    }
  }
Get the value for a attribute on a node. Only used in DEV for SSR validation.
The third argument is used as a hint of what the expected value is. Some
attributes have multiple equivalent values.