Use of CryptoKey with polyfill

This may be an issue of ignorance on my part, if it is please excuse me.

 

I am currently writing some code and have found that one or more of the
algorithms that I need for it are not either on the currently supported or
planned supported list for the browser that I am using.  The way that I
would normally solve this is by doing polyfill for the missing algorithms.
In looking at this I have run into a couple of issues that I am not sure how
to deal with.

 

1.       Is it possible to create a script size class which has the
CryptoKey interface in the prototype chain?  This is one of two issues that
I have (so far) discovered with the use of "instanceof CryptoKey" as a
discriminator in writing my library code.  (The second is the fact that
interfaces which are remoted from a different environment will have this be
false.)  I have not actually tried to write the correct polyfill for this
but have not yet found anything that would support it working either.  My
first guess is that this might be very dependent on how the browser
implements interfaces.

2.       If I want the polyfill to be conditional, then the normal approach
I have seen in the past is to do some type of test on the feature and either
define or not define the polyfill as appropriate.   I am not sure how this
is going to work out with a Promises approach to everything.  Currently the
way that I would think about this is to generate a key with the algorithm in
question.  However given that the result the promise would be pending unless
the algorithm is not in the dictionary to be normalized.   I am also not
sure when the promises would be scheduled relative to the onload event -
would they complete before the onload or would they be potentially
afterwords.  My assumption is that the timing is totally arbitrary.  This
means that the polyfill code may need to be called and started prior to it
finding out if the feature it is filling in for actually exists in the base
implementation. 

 

Help - Jim