1.0.0 • Public • Published


An npm functional programming library project

  1. Fork this repository to your own GitHub account.

  2. Clone your forked version of the lodown repository to a new Cloud9 workspace or locally if you prefer.

  3. To create a package.json configuration file for our lodown library, from the command-line, run the command:

     npm init
  4. IMPORTANT CONFIGURATION: Fill in the prompts with your own details:

    1. When asked for test command, enter:

      istanbul cover _mocha -- test/ -R spec

    2. When asked for your git repository, you will probably be given the correct url as the default, so just select this by pressing return, otherwise, provide your forked GitHub repository's url.

  5. Install the required test libraries by running the following command:

     npm install i -D mocha chai sinon istanbul
  6. Write your tests in the file test/index.spec.js. Check out the chai api for and be careful when asserting/expecting against complex types - you'll have to make use of the .eql api, and not .equal. For example:

     expect(lodown.filter([1, 2, 3], function(value) { return value > 2; } )).to.eql([3]);
  7. Implement your library in the file index.js. Remember that index.js is a Node.js module, so you must export your API using, for example:

     module.exports.each = each;
  8. To run your tests, run the following command:

     npm test
  9. Check the console output for passes and failures.

  10. Preview (Cloud9) or open the file at coverage/lcov-report/index.html for your coverage report. Make certain all lines of code are traversed in your tests!


Using the file at test/fixtures/customers.json, and utilizing your lodown library, write functions that take the Array of customers and return the following:

  1. how many males, how many females
  2. oldest customer, youngest customer
  3. average balance
  4. how many customer's names begin with some letter
  5. how many customer's friend's names begin with some letter
  6. how many customers are friends
  7. how many customers have friends in common
  8. most common tags



  1. https://mochajs.org
  2. http://chaijs.com/api/bdd/
  3. http://sinonjs.org/docs/#spies-api


  1. http://marcofranssen.nl/using-mocha-chai-sinon-to-test-node-js/
  2. http://stackoverflow.com/questions/19298118/what-is-the-role-of-describe-in-mocha
  3. http://www.vapidspace.com/coding/2014/10/29/code-coverage-metrics-with-mocha-and-istanbul/

Quick Videos

  1. https://egghead.io/lessons/javascript-how-to-write-a-javascript-library-setting-up-unit-testing-with-mocha-and-chai
  2. https://egghead.io/lessons/javascript-how-to-write-a-javascript-library-unit-testing-with-mocha-and-chai



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