Jquery determines the existence of child elements    

1. Determine whether a child element exists     // first level child element if($(“#specialId> Img ”). The length = = 0)         If ($(” # specialId: from the (img) ”). The length = = 0)                   {        //— no img submark —        }       Else        {        //— with img submark —        }      

Select a child element of a specific id under a specific id element       $(“#form”). Children (”# t”) so      

Select the child element   under a specific id element;    $(” ul# u> Li :nth-child(2)”) so      

Determine whether an element exists       If ($(” # myId ”). Length> 0)       {          / / there         }