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underbar.html
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<html><head>
<style>
body {
margin: 0 auto;
width: 960px;
}
</style>
</head>
<body>
<h1 id="underbar">Underbar</h1>
<p>This project was written in the same spirit as
<a href="https://github.com/mrdavidlaing/javascript-koans">JavaScript Koans</a>, and thusly
uses the <a href="http://visionmedia.github.io/mocha">Mocha Test Suite</a> to facilitate a
TDD approach to learning. It walks you through a reimplementation of
<a href="http://underscore.js">underscore.js</a>, a popular collection of useful functions
authored by Jeremy Ashkenas.</p>
<h2 id="links-and-resources">Links and Resources</h2>
<p>Some quick notes that may come in handy:</p>
<ul>
<li>As you work through these functions, you may sometimes have questions about
what arguments they take, or about how they work (their <em>interface</em>). If the
inline comments don't clarify these questions, it's a good idea to reference
the official library's <a href="http://underscore.js">documentation</a>.</li>
<li>Many of the functions operate on "collections." They can take both arrays or
objects as their arguments and you need to be able to handle both cases.<ul>
<li>You can use <code>Array.isArray(obj)</code> to find out whether an object is an array.</li>
<li>You can use <code>obj.length</code> to test if something is either a string or an
array.</li>
</ul>
</li></ul>
<h2 id="goals">Goals</h2>
<p>As is, the repository is missing code for most of the functions. It's your job
to fix the library by implementing them. The functions are split in two sections,
with a separate test suite for each.</p>
<p>The files in the <code>spec</code> directory contain the test suites. Your goal is to get all
the tests to pass by implementing the missing functions. Run all the tests by
opening <code>SpecRunner.html</code> in your browser.</p>
<p>The file <code>src/underbar.js</code> contains function definitions and explanations for
the following functions (<em>italicized functions</em> are solved for you). Implement
each of the functions by making all of the tests pass:</p>
<p><strong>Note:</strong> Some browsers provide built-in functions--including <code>forEach</code>, <code>map</code>,
<code>reduce</code> and <code>filter</code>--that replicate the functionality of some of the functions
you will implement. Don't use them to implement your functions.</p>
<h2 id="extra-extra-credit">Extra Extra Credit</h2>
<ul>
<li>Download the real <a href="https://github.com/documentcloud/underscore/">underscore.js</a>
implementation and test suite, and try to understand how it works. A great way
to do this is to break parts of the code and see which tests fail.</li>
<li>Compare your implementations to the ones in the real library. Notice that this
assignment has stripped out some complexity from the original library; notice
where these changes have been made, and try to understand what edge cases the
original library is handling that your functions aren't.</li>
<li>Notice that the real underscore.js uses an object named <code>breaker</code>. Look through the
source and understand what this is doing, and how it optimizes some of the functions.</li>
</ul>
</body></html>