if your using event handlers, select it and view all properties in designer, there are 3 events "onComplete", "onError", "onStart" that can be used.

 

if you mean raw SSJS somewhere on a page, its the same as standard JS 

 

try 

{

   // code that will throw error

} 

catch(err) 

{

   // some code to handle, e.g. redirect to page that has error message, try something else etc.

}