Enforcing the usage of new

[AlexisTM]

As the new keyword is mandatory, the usage should be enforced.

The current stage is that the event dispatch fails if you forget the new but it is not clear why. Adding a check that new has been used can give a meaningful error instead.

The shortest way seems to be the following:

if (!(this instanceof RobustWebSocket))
    throw new Error('Constructor called without new');