If I have a javascript class which cannot be instantiated what should the constructor return that I can test for. The constructor always returns an object so I cannot return null if the constructor fails.

function SomeClass(id) {

  if(typeof(id) === 'number' {

    // This is good

    this.id = id;

  } else {

    // This is bad

    // This return is ignored and an empty object is returned

    return null;

  }

}



var a = new SomeClass('badParam');

if(a){

  // is true even though the class expects a number.

}



// Could use this check

if(a.id !== undefined){

  // Do some stuff

}

but it seems there should be a better way.