Compile Time Type Checking

ClojureScript can easily leverage Google Closure for compile time type checking. This is done simply via ClojureScript docstrings which are compiled into JSDoc style comment blocks. Google Closure supports many useful kinds of type annotation. For example you can write a function that takes non-nullable Object.

(defn foo 
  "@param {!Object} x
  [x] x)

If Closure can infer that some invoke may pass null, this will result in a compile time type error.