exercism fetch javascript strain


Implement the keep and discard operation on collections. Given a collection and a predicate on the collection's elements, keep returns a new collection containing those elements where the predicate is true, while discard returns a new collection containing those elements where the predicate is false.

For example, given the collection of numbers:

And the predicate:

Then your keep operation should produce:

While your discard operation should produce:

Note that the union of keep and discard is all the elements.

The functions may be called keep and discard, or they may need different names in order to not clash with existing functions or concepts in your language.


Keep your hands off that filter/reject/whatchamacallit functionality provided by your standard library! Solve this one yourself using other basic tools instead.


Go through the setup instructions for JavaScript to install the necessary dependencies:


Running the test suite

The provided test suite uses Jasmine. You can install it by opening a terminal window and running the following command:

npm install -g jasmine

Run the test suite from the exercise directory with:

jasmine strain.spec.js

In many test suites all but the first test have been marked "pending". Once you get a test passing, activate the next one by changing xit to it.


Conversation with James Edward Gray II https://twitter.com/jeg2

Submitting Incomplete Solutions

It's possible to submit an incomplete solution so you can see how others have completed the exercise.