in this case li id is menu-item-1002 .
this id is auto generated by wordpress and always unique. So the every wordpress menu url id is unique
Step 3. Place the following code before the end of head tag (open header.php find </head>) of current theme and put you menu id in highlighted area.
Here Is the script that you need to add in header.php of your wordpress current theme, before the end of head tag (</head>).
var menuID = jQuery(‘#your menu id’);
findA = menuID.find(‘a’);
For Plugin see: Updated Post [ onclick on Wordpress Menu- Plugin ]