javascript - How to exit / return from class as null -

usually in other languages looks nullreferenceexception, don't know how in js, beginner knowledge of c# - not js

<script>     var x = new fooclass(null);      function fooclass(foo)     {         if(foo===null)             return;     // return type "fooclass"                         // want return tell                         // class wrong initialized, maybe exception?          alert(foo); // show script continues     } </script> 

yes. exactly. can throw exception stating error message

if(foo === null)    throw "null not allowed" // throw exception message 

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