how do i get the id under another id in an if statement?

how do i get the id under another id in an if statement?

$('#mainmenu').mouseenter(function ()开发者_如何学编程 {
  if ( $(this).???('#a')) {
        }  

  if ( $(this).???('#b')) {
        }  
});

<div id="mainmenu">
    <div id="a"></div>
    <div id="b"></div>
</div>

You want the find method.

$(this).find('#a')

$('#mainmenu #a, #mainmenu #b').mouseenter(function(){
 // code for something cool...
});

HTH.

Try this:

$('#mainmenu').mouseenter(function () {

  if ($('#a', $(this)) {
    // your code here...............
  }  

  if ($('#b', $(this)) {
    // your code here...............
  }  

});