Check JS Foundations for tests requiring impurity

[wvmitchell]

Description

In seeing students solve the current (new) JS foundations, some of the tests cannot be passed without creating an impure function. None of the tests should require this.

Summary of Changes

• Solve all the existing JS foundations, looking for spaces where the test cannot be solved without creating an impure function
• Refactor/replace any tests that require the creation of an impure function

Note

• Testing for the side effect of a function is an example of this. If you encounter a test where it is expected that something has changed as the result of running a function, but that function didn't return anything, it's a side effect, and needs to go away.