The typescript code base needs to be distributed in compiled form for user's to be able to use it. Our prepare script should run and conditionally compile when a src directory is present and tsc is available. 
Situations to consider:

• A contributor clones and runs npm install to get dependencies, this should compile the driver
• A user npm installs the driver, no src is present, tsc is a dev dep (they could be using typescript so it might be present)
• A user specifies a git revision as a version number, this is not precisely a supported downstream method but it would be good to not dump error messages in this use case either