unexpected

<!DOCTYPE html> <html> <head> <meta charset="utf-8"> <meta name="viewport" content="width=device-width,initial-scale=1,maximum-scale=1,user-scalable=0"> <link rel="stylesheet" href="../../static/normalize.css" type="text/css" media="screen" /> <link rel="stylesheet" href="../../static/main.css" type="text/css" media="screen" /> <link rel="shortcut icon" type="image/vnd.microsoft.icon" href="../../static/bug-icon-black.ico"> <title>addType</title> </head> <body class="sidebar-hidden has-sidebar"> <header> <div class="logo-icon"></div> <nav> <ul> <li class="menu-toggle-item"> <button class="menu-toggle" onclick="toggleSidebar()"></button> </li> <li class=""><a href="../..">Unexpected</a></li> <li class=""><a href="../../assertions/any/to-be">Assertions</a></li> <li class="active"><a href="../addAssertion">API</a></li> <li class=""><a href="../../plugins">Plugins</a></li> </ul> </nav> <div class="search" style="visibility: hidden"> <input id="search" placeholder="Search..." value=""> <div id="searchDropDown" class="dropDown"> <ul id="searchResults"></ul> </div> </div> </header> <section id="api"> <nav id="api-menu" class="sidebar js-remember-scroll-position"> <ul> <li class=""> <a href="../addAssertion">addAssertion</a> </li> <li class="active"> <a href="">addType</a> </li> <li class=""> <a href="../async">async</a> </li> <li class=""> <a href="../clone">clone</a> </li> <li class=""> <a href="../expect">expect</a> </li> <li class=""> <a href="../fail">fail</a> </li> <li class=""> <a href="../promise">promise</a> </li> <li class=""> <a href="../promise-all">promise.all</a> </li> <li class=""> <a href="../promise-any">promise.any</a> </li> <li class=""> <a href="../promise-settle">promise.settle</a> </li> <li class=""> <a href="../toString">toString</a> </li> <li class=""> <a href="../UnexpectedError">UnexpectedError</a> </li> <li class=""> <a href="../use">use</a> </li> <li class=""> <a href="../withError">withError</a> </li> </ul> </nav> <div class="main" tabindex="-1"> <div class="content"> <h1 id="types">Types</h1> <p>Unexpected comes with a type system that is used to explain how different types are compared, diffed, inspected and is also used to limit the scope of assertions.</p> <p>The following types are provided by out of the box by Unexpected: <code>any</code>, <code>arguments</code>, <code>array</code>, <code>array-like</code>, <code>binaryArray</code>, <code>boolean</code>, <code>Buffer</code>, <code>date</code>, <code>Error</code>, <code>function</code>, <code>Int8Array</code>, <code>Int16Array</code>, <code>Int32Array</code>, <code>NaN</code>, <code>null</code>, <code>number</code>, <code>object</code>, <code>regexp</code>, <code>string</code>, <code>Uint8Array</code>, <code>Uint16Array</code>, <code>Uint32Array</code>, and <code>undefined</code>.</p> <h2 id="expect-addtype-typedefinition-">expect.addType(typeDefinition)</h2> <p>Unexpected can be extended with knowledge about new types by calling the <code>addType</code> method with a type definition. The type definition must implement the required parts of the following interface:</p> <p>Required members:</p> <ul> <li><strong>name</strong>: <code>String</code> - the name of the type.</li> <li><strong>identify</strong>: <code>boolean function(value)</code> - a function deciding if the type should be used for the given value.</li> </ul> <p>Note that your type has the option to take precedence over all the built-in types. Test subjects will be tested against the most recently defined type first, so <code>identify</code> functions should take care not to break with <code>undefined</code>, <code>null</code> and so on.</p> <p>Optional members:</p> <ul> <li><strong>base</strong>: <code>String</code> - the name of the base type. Defaults to <code>any</code>.</li> <li><strong>equal</strong>: <code>boolean function(a, b, equal)</code> - a function capable of comparing two values of this type for equality. If not specified it is inherited from the base type.</li> <li><strong>inspect</strong>: <code>function(value, depth, output, inspect)</code> - a function capable of inspecting a value of this type. If not specified it is inherited from the base type.</li> <li><strong>diff</strong>: <code>comparison function(actual, expected, output, diff, inspect)</code> - a function producing a comparison between two values of this type. If not specified it is inherited from the base type.</li> </ul> <h2 id="example">Example</h2> <p>Adding new types to the system is best explained by an example. Let's say we wanted to add first class support for a <code>Person</code> type:</p> <div class="code lang-javascript"> <div><span style="color: #a71d5d">function</span> <span style="color: #000000">Person</span><span style="color: #000000">(</span>name<span style="color: #000000">,</span> age<span style="color: #000000">)</span> <span style="color: #000000">{</span></div> <div>    <span style="color: #a71d5d">this</span><span style="color: #000000">.</span>name <span style="color: #a71d5d">=</span> name<span style="color: #000000">;</span></div> <div>    <span style="color: #a71d5d">this</span><span style="color: #000000">.</span>age <span style="color: #a71d5d">=</span> age<span style="color: #000000">;</span></div> <div><span style="color: #000000">}</span></div> </div><p>We start out by creating a basic type for handling <code>Person</code> instances. The name of the type should be <code>Person</code> and it should inherit from the built-in <code>object</code> type. Furthermore we add an <code>identify</code> method that will recognize <code>Person</code> instances.</p> <div class="code lang-javascript"> <div>expect<span style="color: #000000">.</span><span style="color: #000000">addType</span><span style="color: #000000">({</span></div> <div>    name<span style="color: #000000">:</span> <span style="color: #df5000">'Person'</span><span style="color: #000000">,</span></div> <div>    base<span style="color: #000000">:</span> <span style="color: #df5000">'object'</span><span style="color: #000000">,</span></div> <div>    identify<span style="color: #000000">:</span> <span style="color: #a71d5d">function</span> <span style="color: #000000">(</span>value<span style="color: #000000">)</span> <span style="color: #000000">{</span></div> <div>        <span style="color: #a71d5d">return</span> value <span style="color: #a71d5d">instanceof</span> Person<span style="color: #000000">;</span></div> <div>    <span style="color: #000000">}</span></div> <div><span style="color: #000000">});</span></div> </div><p>When you specify a base type, you inherit the optional members you didn't implement. In this case we inherited the methods <code>equal</code>, <code>inspect</code> and <code>diff</code> from the <code>object</code> type.</p> <p>Imagine that we make a failing expectation on a <code>Person</code> instance:</p> <div class="code lang-javascript"> <div><span style="color: #000000">expect</span><span style="color: #000000">(</span><span style="color: #a71d5d">new</span> Person<span style="color: #000000">(</span><span style="color: #df5000">'John Doe'</span><span style="color: #000000">,</span> <span style="color: #0086b3">42</span><span style="color: #000000">),</span> <span style="color: #df5000">'to equal'</span><span style="color: #000000">,</span> <span style="color: #a71d5d">new</span> Person<span style="color: #000000">(</span><span style="color: #df5000">'Jane Doe'</span><span style="color: #000000">,</span> <span style="color: #0086b3">24</span><span style="color: #000000">));</span></div> </div><div class="output"> <div><span style="color: red; font-weight: bold">expected</span> Person({ <span style="color: #555">name</span>: <span style="color: #df5000">'John Doe'</span>, <span style="color: #555">age</span>: <span style="color: #0086b3">42</span> })</div> <div><span style="color: red; font-weight: bold">to equal</span> Person({ <span style="color: #555">name</span>: <span style="color: #df5000">'Jane Doe'</span>, <span style="color: #555">age</span>: <span style="color: #0086b3">24</span> })</div> <div> </div> <div>Person({</div> <div>  <div style="display: inline-block; vertical-align: top"> <div><span style="color: #555">name</span>: <div style="display: inline-block; vertical-align: top"> <div><span style="color: #df5000">'John Doe'</span>,</div> </div> <div style="display: inline-block; vertical-align: top"> <div><span style="color: red; font-weight: bold">//</span></div> <div><span style="color: red; font-weight: bold">//</span></div> <div><span style="color: red; font-weight: bold">//</span></div> </div> <div style="display: inline-block; vertical-align: top"> <div><span style="color: red; font-weight: bold">should equal</span> <div style="display: inline-block; vertical-align: top"> <div><span style="color: #df5000">'Jane Doe'</span></div> </div></div> <div><div style="display: inline-block; vertical-align: top"> <div><span style="color: red">-</span></div> </div><div style="display: inline-block; vertical-align: top"> <div><span style="background-color: red; color: white">John</span><span style="color: red"> Doe</span></div> </div></div> <div><div style="display: inline-block; vertical-align: top"> <div><span style="color: green">+</span></div> </div><div style="display: inline-block; vertical-align: top"> <div><span style="background-color: green; color: white">Jane</span><span style="color: green"> Doe</span></div> </div></div> </div></div> </div></div> <div>  <div style="display: inline-block; vertical-align: top"> <div><span style="color: #555">age</span>: <div style="display: inline-block; vertical-align: top"> <div><span style="color: #0086b3">42</span></div> </div> <div style="display: inline-block; vertical-align: top"> <div><span style="color: red; font-weight: bold">//</span></div> </div> <div style="display: inline-block; vertical-align: top"> <div><span style="color: red; font-weight: bold">should equal</span> <div style="display: inline-block; vertical-align: top"> <div><span style="color: #0086b3">24</span></div> </div></div> </div></div> </div></div> <div>})</div> </div><p>That is already quite helpful, but it would be even nicer if the stringification of <code>Person</code> instances could read as valid calls to the constructor. We can fix that by implementing an <code>inspect</code> method on the type.</p> <div class="code lang-javascript"> <div>expect<span style="color: #000000">.</span><span style="color: #000000">addType</span><span style="color: #000000">({</span></div> <div>    name<span style="color: #000000">:</span> <span style="color: #df5000">'Person'</span><span style="color: #000000">,</span></div> <div>    base<span style="color: #000000">:</span> <span style="color: #df5000">'object'</span><span style="color: #000000">,</span></div> <div>    identify<span style="color: #000000">:</span> <span style="color: #a71d5d">function</span> <span style="color: #000000">(</span>value<span style="color: #000000">)</span> <span style="color: #000000">{</span></div> <div>        <span style="color: #a71d5d">return</span> value <span style="color: #a71d5d">instanceof</span> Person<span style="color: #000000">;</span></div> <div>    <span style="color: #000000">},</span></div> <div>    inspect<span style="color: #000000">:</span> <span style="color: #a71d5d">function</span> <span style="color: #000000">(</span>person<span style="color: #000000">,</span> depth<span style="color: #000000">,</span> output<span style="color: #000000">,</span> inspect<span style="color: #000000">)</span> <span style="color: #000000">{</span></div> <div>       output<span style="color: #000000">.</span><span style="color: #000000">text</span><span style="color: #000000">(</span><span style="color: #df5000">'new Person('</span><span style="color: #000000">)</span></div> <div>             <span style="color: #000000">.</span><span style="color: #000000">append</span><span style="color: #000000">(</span><span style="color: #000000">inspect</span><span style="color: #000000">(</span>person<span style="color: #000000">.</span>name<span style="color: #000000">,</span> depth<span style="color: #000000">))</span></div> <div>             <span style="color: #000000">.</span><span style="color: #000000">text</span><span style="color: #000000">(</span><span style="color: #df5000">', '</span><span style="color: #000000">)</span></div> <div>             <span style="color: #000000">.</span><span style="color: #000000">append</span><span style="color: #000000">(</span><span style="color: #000000">inspect</span><span style="color: #000000">(</span>person<span style="color: #000000">.</span>age<span style="color: #000000">,</span> depth<span style="color: #000000">))</span></div> <div>             <span style="color: #000000">.</span><span style="color: #000000">text</span><span style="color: #000000">(</span><span style="color: #df5000">')'</span><span style="color: #000000">);</span></div> <div>    <span style="color: #000000">}</span></div> <div><span style="color: #000000">});</span></div> </div><p>Now we get the following output:</p> <div class="code lang-javascript"> <div><span style="color: #000000">expect</span><span style="color: #000000">(</span><span style="color: #a71d5d">new</span> Person<span style="color: #000000">(</span><span style="color: #df5000">'John Doe'</span><span style="color: #000000">,</span> <span style="color: #0086b3">42</span><span style="color: #000000">),</span> <span style="color: #df5000">'to equal'</span><span style="color: #000000">,</span> <span style="color: #a71d5d">new</span> Person<span style="color: #000000">(</span><span style="color: #df5000">'Jane Doe'</span><span style="color: #000000">,</span> <span style="color: #0086b3">24</span><span style="color: #000000">));</span></div> </div><div class="output"> <div><span style="color: red; font-weight: bold">expected</span> new Person(<span style="color: #df5000">'John Doe'</span>, <span style="color: #0086b3">42</span>) <span style="color: red; font-weight: bold">to equal</span> new Person(<span style="color: #df5000">'Jane Doe'</span>, <span style="color: #0086b3">24</span>)</div> <div> </div> <div>Person({</div> <div>  <div style="display: inline-block; vertical-align: top"> <div><span style="color: #555">name</span>: <div style="display: inline-block; vertical-align: top"> <div><span style="color: #df5000">'John Doe'</span>,</div> </div> <div style="display: inline-block; vertical-align: top"> <div><span style="color: red; font-weight: bold">//</span></div> <div><span style="color: red; font-weight: bold">//</span></div> <div><span style="color: red; font-weight: bold">//</span></div> </div> <div style="display: inline-block; vertical-align: top"> <div><span style="color: red; font-weight: bold">should equal</span> <div style="display: inline-block; vertical-align: top"> <div><span style="color: #df5000">'Jane Doe'</span></div> </div></div> <div><div style="display: inline-block; vertical-align: top"> <div><span style="color: red">-</span></div> </div><div style="display: inline-block; vertical-align: top"> <div><span style="background-color: red; color: white">John</span><span style="color: red"> Doe</span></div> </div></div> <div><div style="display: inline-block; vertical-align: top"> <div><span style="color: green">+</span></div> </div><div style="display: inline-block; vertical-align: top"> <div><span style="background-color: green; color: white">Jane</span><span style="color: green"> Doe</span></div> </div></div> </div></div> </div></div> <div>  <div style="display: inline-block; vertical-align: top"> <div><span style="color: #555">age</span>: <div style="display: inline-block; vertical-align: top"> <div><span style="color: #0086b3">42</span></div> </div> <div style="display: inline-block; vertical-align: top"> <div><span style="color: red; font-weight: bold">//</span></div> </div> <div style="display: inline-block; vertical-align: top"> <div><span style="color: red; font-weight: bold">should equal</span> <div style="display: inline-block; vertical-align: top"> <div><span style="color: #0086b3">24</span></div> </div></div> </div></div> </div></div> <div>})</div> </div><p>That is a bit better, let me explain how it works. The <code>inspect</code> method is called with the value to be inspected, the depth this type should be inspected with, an output the inspected value should be written to, and an inspect function that can be used to recursively inspect members. The output is an instance of <a href="https://github.com/unexpectedjs/magicpen">magicpen</a> extended with a number of <a href="https://github.com/unexpectedjs/unexpected/blob/master/lib/styles.js">styles</a>.</p> <p>We write <code>new Person(</code> without styling, then we append the inspected <code>name</code>, write a <code>,</code>, inspect the <code>age</code> and finish with the closing parenthesis. When <code>inspect</code> is called without a depth parameter it defaults to <code>depth-1</code>. Values inspected with depth zero will be inspected as <code>...</code>. In this case we always want the name so we forward the same depth to the <code>inspect</code> function.</p> <p>Let's say we wanted <code>Person</code> instances only to be compared by name and not by age. Then we need to override the <code>equal</code> method:</p> <div class="code lang-javascript"> <div>expect<span style="color: #000000">.</span><span style="color: #000000">addType</span><span style="color: #000000">({</span></div> <div>    name<span style="color: #000000">:</span> <span style="color: #df5000">'Person'</span><span style="color: #000000">,</span></div> <div>    base<span style="color: #000000">:</span> <span style="color: #df5000">'object'</span><span style="color: #000000">,</span></div> <div>    identify<span style="color: #000000">:</span> <span style="color: #a71d5d">function</span> <span style="color: #000000">(</span>value<span style="color: #000000">)</span> <span style="color: #000000">{</span></div> <div>        <span style="color: #a71d5d">return</span> value <span style="color: #a71d5d">instanceof</span> Person<span style="color: #000000">;</span></div> <div>    <span style="color: #000000">},</span></div> <div>    inspect<span style="color: #000000">:</span> <span style="color: #a71d5d">function</span> <span style="color: #000000">(</span>person<span style="color: #000000">,</span> depth<span style="color: #000000">,</span> output<span style="color: #000000">,</span> inspect<span style="color: #000000">)</span> <span style="color: #000000">{</span></div> <div>       output<span style="color: #000000">.</span><span style="color: #000000">text</span><span style="color: #000000">(</span><span style="color: #df5000">'new Person('</span><span style="color: #000000">)</span></div> <div>             <span style="color: #000000">.</span><span style="color: #000000">append</span><span style="color: #000000">(</span><span style="color: #000000">inspect</span><span style="color: #000000">(</span>person<span style="color: #000000">.</span>name<span style="color: #000000">,</span> depth<span style="color: #000000">))</span></div> <div>             <span style="color: #000000">.</span><span style="color: #000000">text</span><span style="color: #000000">(</span><span style="color: #df5000">', '</span><span style="color: #000000">)</span></div> <div>             <span style="color: #000000">.</span><span style="color: #000000">append</span><span style="color: #000000">(</span><span style="color: #000000">inspect</span><span style="color: #000000">(</span>person<span style="color: #000000">.</span>age<span style="color: #000000">,</span> depth<span style="color: #000000">))</span></div> <div>             <span style="color: #000000">.</span><span style="color: #000000">text</span><span style="color: #000000">(</span><span style="color: #df5000">')'</span><span style="color: #000000">);</span></div> <div>    <span style="color: #000000">},</span></div> <div>    equal<span style="color: #000000">:</span> <span style="color: #a71d5d">function</span> <span style="color: #000000">(</span>a<span style="color: #000000">,</span> b<span style="color: #000000">,</span> equal<span style="color: #000000">)</span> <span style="color: #000000">{</span></div> <div>        <span style="color: #a71d5d">return</span> a <span style="color: #a71d5d">===</span> b <span style="color: #a71d5d">||</span> <span style="color: #000000">equal</span><span style="color: #000000">(</span>a<span style="color: #000000">.</span>name<span style="color: #000000">,</span> b<span style="color: #000000">.</span>name<span style="color: #000000">);</span></div> <div>    <span style="color: #000000">}</span></div> <div><span style="color: #000000">});</span></div> </div><p>This will produce the same output as above, but that means the diff if wrong. It states that the age should be changed. We can fix that the following way:</p> <div class="code lang-javascript"> <div>expect<span style="color: #000000">.</span><span style="color: #000000">addType</span><span style="color: #000000">({</span></div> <div>    name<span style="color: #000000">:</span> <span style="color: #df5000">'Person'</span><span style="color: #000000">,</span></div> <div>    base<span style="color: #000000">:</span> <span style="color: #df5000">'object'</span><span style="color: #000000">,</span></div> <div>    identify<span style="color: #000000">:</span> <span style="color: #a71d5d">function</span> <span style="color: #000000">(</span>value<span style="color: #000000">)</span> <span style="color: #000000">{</span></div> <div>        <span style="color: #a71d5d">return</span> value <span style="color: #a71d5d">instanceof</span> Person<span style="color: #000000">;</span></div> <div>    <span style="color: #000000">},</span></div> <div>    inspect<span style="color: #000000">:</span> <span style="color: #a71d5d">function</span> <span style="color: #000000">(</span>person<span style="color: #000000">,</span> depth<span style="color: #000000">,</span> output<span style="color: #000000">,</span> inspect<span style="color: #000000">)</span> <span style="color: #000000">{</span></div> <div>       output<span style="color: #000000">.</span><span style="color: #000000">text</span><span style="color: #000000">(</span><span style="color: #df5000">'new Person('</span><span style="color: #000000">)</span></div> <div>             <span style="color: #000000">.</span><span style="color: #000000">append</span><span style="color: #000000">(</span><span style="color: #000000">inspect</span><span style="color: #000000">(</span>person<span style="color: #000000">.</span>name<span style="color: #000000">,</span> depth<span style="color: #000000">))</span></div> <div>             <span style="color: #000000">.</span><span style="color: #000000">text</span><span style="color: #000000">(</span><span style="color: #df5000">', '</span><span style="color: #000000">)</span></div> <div>             <span style="color: #000000">.</span><span style="color: #000000">append</span><span style="color: #000000">(</span><span style="color: #000000">inspect</span><span style="color: #000000">(</span>person<span style="color: #000000">.</span>age<span style="color: #000000">,</span> depth<span style="color: #000000">))</span></div> <div>             <span style="color: #000000">.</span><span style="color: #000000">text</span><span style="color: #000000">(</span><span style="color: #df5000">')'</span><span style="color: #000000">);</span></div> <div>    <span style="color: #000000">},</span></div> <div>    equal<span style="color: #000000">:</span> <span style="color: #a71d5d">function</span> <span style="color: #000000">(</span>a<span style="color: #000000">,</span> b<span style="color: #000000">,</span> equal<span style="color: #000000">)</span> <span style="color: #000000">{</span></div> <div>        <span style="color: #a71d5d">return</span> a <span style="color: #a71d5d">===</span> b <span style="color: #a71d5d">||</span> <span style="color: #000000">equal</span><span style="color: #000000">(</span>a<span style="color: #000000">.</span>name<span style="color: #000000">,</span> b<span style="color: #000000">.</span>name<span style="color: #000000">);</span></div> <div>    <span style="color: #000000">},</span></div> <div>    diff<span style="color: #000000">:</span> <span style="color: #a71d5d">function</span> <span style="color: #000000">(</span>actual<span style="color: #000000">,</span> expected<span style="color: #000000">,</span> output<span style="color: #000000">,</span> diff<span style="color: #000000">,</span> inspect<span style="color: #000000">)</span> <span style="color: #000000">{</span></div> <div>        <span style="color: #a71d5d">return</span> <span style="color: #a71d5d">this</span><span style="color: #000000">.</span>baseType<span style="color: #000000">.</span><span style="color: #000000">diff</span><span style="color: #000000">({</span>name<span style="color: #000000">:</span> actual<span style="color: #000000">.</span>name<span style="color: #000000">},</span> <span style="color: #000000">{</span>name<span style="color: #000000">:</span> expected<span style="color: #000000">.</span>name<span style="color: #000000">},</span> output<span style="color: #000000">);</span></div> <div>    <span style="color: #000000">}</span></div> <div><span style="color: #000000">});</span></div> </div><div class="code lang-javascript"> <div><span style="color: #000000">expect</span><span style="color: #000000">(</span><span style="color: #a71d5d">new</span> Person<span style="color: #000000">(</span><span style="color: #df5000">'John Doe'</span><span style="color: #000000">,</span> <span style="color: #0086b3">42</span><span style="color: #000000">),</span> <span style="color: #df5000">'to equal'</span><span style="color: #000000">,</span> <span style="color: #a71d5d">new</span> Person<span style="color: #000000">(</span><span style="color: #df5000">'Jane Doe'</span><span style="color: #000000">,</span> <span style="color: #0086b3">24</span><span style="color: #000000">));</span></div> </div><div class="output"> <div><span style="color: red; font-weight: bold">expected</span> new Person(<span style="color: #df5000">'John Doe'</span>, <span style="color: #0086b3">42</span>) <span style="color: red; font-weight: bold">to equal</span> new Person(<span style="color: #df5000">'Jane Doe'</span>, <span style="color: #0086b3">24</span>)</div> <div> </div> <div>{</div> <div>  <div style="display: inline-block; vertical-align: top"> <div><span style="color: #555">name</span>: <div style="display: inline-block; vertical-align: top"> <div><span style="color: #df5000">'John Doe'</span></div> </div> <div style="display: inline-block; vertical-align: top"> <div><span style="color: red; font-weight: bold">//</span></div> <div><span style="color: red; font-weight: bold">//</span></div> <div><span style="color: red; font-weight: bold">//</span></div> </div> <div style="display: inline-block; vertical-align: top"> <div><span style="color: red; font-weight: bold">should equal</span> <div style="display: inline-block; vertical-align: top"> <div><span style="color: #df5000">'Jane Doe'</span></div> </div></div> <div><div style="display: inline-block; vertical-align: top"> <div><span style="color: red">-</span></div> </div><div style="display: inline-block; vertical-align: top"> <div><span style="background-color: red; color: white">John</span><span style="color: red"> Doe</span></div> </div></div> <div><div style="display: inline-block; vertical-align: top"> <div><span style="color: green">+</span></div> </div><div style="display: inline-block; vertical-align: top"> <div><span style="background-color: green; color: white">Jane</span><span style="color: green"> Doe</span></div> </div></div> </div></div> </div></div> <div>}</div> </div><p>The above <code>diff</code> method just calls the <code>diff</code> method on the base type with objects that only contain the name. The <code>object</code> diff will take care of all the hard work. We could also have called the <code>diff</code> function we got as an argument, but that will go off detecting the types of the parameters, therefore it is faster to call <code>diff</code> method on the base directly when you know it is the one you need.</p> <p>You could also do something really custom as seen below:</p> <div class="code lang-javascript"> <div><span style="color: #a71d5d">var</span> inlineDiff <span style="color: #a71d5d">=</span> <span style="color: #0086b3">true</span><span style="color: #000000">;</span><span style="color: #969896"> // used to change inlining in a later example</span></div> <div> </div> <div>expect<span style="color: #000000">.</span><span style="color: #000000">addType</span><span style="color: #000000">({</span></div> <div>    name<span style="color: #000000">:</span> <span style="color: #df5000">'Person'</span><span style="color: #000000">,</span></div> <div>    base<span style="color: #000000">:</span> <span style="color: #df5000">'object'</span><span style="color: #000000">,</span></div> <div>    identify<span style="color: #000000">:</span> <span style="color: #a71d5d">function</span> <span style="color: #000000">(</span>value<span style="color: #000000">)</span> <span style="color: #000000">{</span></div> <div>        <span style="color: #a71d5d">return</span> value <span style="color: #a71d5d">instanceof</span> Person<span style="color: #000000">;</span></div> <div>    <span style="color: #000000">},</span></div> <div>    inspect<span style="color: #000000">:</span> <span style="color: #a71d5d">function</span> <span style="color: #000000">(</span>person<span style="color: #000000">,</span> depth<span style="color: #000000">,</span> output<span style="color: #000000">,</span> inspect<span style="color: #000000">)</span> <span style="color: #000000">{</span></div> <div>       output<span style="color: #000000">.</span><span style="color: #000000">text</span><span style="color: #000000">(</span><span style="color: #df5000">'new Person('</span><span style="color: #000000">)</span></div> <div>             <span style="color: #000000">.</span><span style="color: #000000">append</span><span style="color: #000000">(</span><span style="color: #000000">inspect</span><span style="color: #000000">(</span>person<span style="color: #000000">.</span>name<span style="color: #000000">,</span> depth<span style="color: #000000">))</span></div> <div>             <span style="color: #000000">.</span><span style="color: #000000">text</span><span style="color: #000000">(</span><span style="color: #df5000">', '</span><span style="color: #000000">)</span></div> <div>             <span style="color: #000000">.</span><span style="color: #000000">append</span><span style="color: #000000">(</span><span style="color: #000000">inspect</span><span style="color: #000000">(</span>person<span style="color: #000000">.</span>age<span style="color: #000000">,</span> depth<span style="color: #000000">))</span></div> <div>             <span style="color: #000000">.</span><span style="color: #000000">text</span><span style="color: #000000">(</span><span style="color: #df5000">')'</span><span style="color: #000000">);</span></div> <div>    <span style="color: #000000">},</span></div> <div>    equal<span style="color: #000000">:</span> <span style="color: #a71d5d">function</span> <span style="color: #000000">(</span>a<span style="color: #000000">,</span> b<span style="color: #000000">,</span> equal<span style="color: #000000">)</span> <span style="color: #000000">{</span></div> <div>        <span style="color: #a71d5d">return</span> a <span style="color: #a71d5d">===</span> b <span style="color: #a71d5d">||</span> <span style="color: #000000">equal</span><span style="color: #000000">(</span>a<span style="color: #000000">.</span>name<span style="color: #000000">,</span> b<span style="color: #000000">.</span>name<span style="color: #000000">);</span></div> <div>    <span style="color: #000000">},</span></div> <div>    diff<span style="color: #000000">:</span> <span style="color: #a71d5d">function</span> <span style="color: #000000">(</span>actual<span style="color: #000000">,</span> expected<span style="color: #000000">,</span> output<span style="color: #000000">,</span> diff<span style="color: #000000">,</span> inspect<span style="color: #000000">)</span> <span style="color: #000000">{</span></div> <div>        <span style="color: #a71d5d">var</span> nameDiff <span style="color: #a71d5d">=</span> <span style="color: #000000">diff</span><span style="color: #000000">(</span>actual<span style="color: #000000">.</span>name<span style="color: #000000">,</span> expected<span style="color: #000000">.</span>name<span style="color: #000000">);</span></div> <div> </div> <div>        output<span style="color: #000000">.</span><span style="color: #000000">text</span><span style="color: #000000">(</span><span style="color: #df5000">'new Person('</span><span style="color: #000000">)</span></div> <div>              <span style="color: #000000">.</span><span style="color: #000000">nl</span><span style="color: #000000">()</span></div> <div>              <span style="color: #000000">.</span><span style="color: #000000">indentLines</span><span style="color: #000000">();</span></div> <div> </div> <div>        <span style="color: #a71d5d">if</span> <span style="color: #000000">(</span>nameDiff && nameDiff<span style="color: #000000">.</span>inline<span style="color: #000000">)</span> <span style="color: #000000">{</span></div> <div>            output<span style="color: #000000">.</span><span style="color: #000000">append</span><span style="color: #000000">(</span>nameDiff<span style="color: #000000">.</span>diff<span style="color: #000000">);</span></div> <div>        <span style="color: #000000">}</span> <span style="color: #a71d5d">else</span> <span style="color: #000000">{</span></div> <div>            output<span style="color: #000000">.</span><span style="color: #000000">i</span><span style="color: #000000">().</span><span style="color: #000000">append</span><span style="color: #000000">(</span><span style="color: #000000">inspect</span><span style="color: #000000">(</span>actual<span style="color: #000000">.</span>name<span style="color: #000000">)).</span><span style="color: #000000">text</span><span style="color: #000000">(</span><span style="color: #df5000">','</span><span style="color: #000000">).</span><span style="color: #000000">sp</span><span style="color: #000000">()</span></div> <div>                  <span style="color: #000000">.</span><span style="color: #000000">annotationBlock</span><span style="color: #000000">(</span><span style="color: #a71d5d">function</span> <span style="color: #000000">()</span> <span style="color: #000000">{</span></div> <div>                      <span style="color: #a71d5d">this</span><span style="color: #000000">.</span><span style="color: #000000">error</span><span style="color: #000000">(</span><span style="color: #df5000">'should be '</span><span style="color: #000000">).</span><span style="color: #000000">append</span><span style="color: #000000">(</span><span style="color: #000000">inspect</span><span style="color: #000000">(</span>expected<span style="color: #000000">.</span>name<span style="color: #000000">));</span></div> <div>                      <span style="color: #a71d5d">if</span> <span style="color: #000000">(</span>nameDiff<span style="color: #000000">)</span> <span style="color: #000000">{</span></div> <div>                          <span style="color: #a71d5d">this</span><span style="color: #000000">.</span><span style="color: #000000">nl</span><span style="color: #000000">().</span><span style="color: #000000">append</span><span style="color: #000000">(</span>nameDiff<span style="color: #000000">.</span>diff<span style="color: #000000">);</span></div> <div>                      <span style="color: #000000">}</span></div> <div>                  <span style="color: #000000">})</span></div> <div>                  <span style="color: #000000">.</span><span style="color: #000000">nl</span><span style="color: #000000">();</span></div> <div>        <span style="color: #000000">}</span></div> <div> </div> <div>        output<span style="color: #000000">.</span><span style="color: #000000">i</span><span style="color: #000000">().</span><span style="color: #000000">append</span><span style="color: #000000">(</span><span style="color: #000000">inspect</span><span style="color: #000000">(</span>actual<span style="color: #000000">.</span>age<span style="color: #000000">))</span></div> <div>              <span style="color: #000000">.</span><span style="color: #000000">outdentLines</span><span style="color: #000000">()</span></div> <div>              <span style="color: #000000">.</span><span style="color: #000000">nl</span><span style="color: #000000">()</span></div> <div>              <span style="color: #000000">.</span><span style="color: #000000">text</span><span style="color: #000000">(</span><span style="color: #df5000">')'</span><span style="color: #000000">);</span></div> <div> </div> <div>        <span style="color: #a71d5d">return</span> <span style="color: #000000">{</span></div> <div>            inline<span style="color: #000000">:</span> inlineDiff<span style="color: #000000">,</span></div> <div>            diff<span style="color: #000000">:</span> output</div> <div>        <span style="color: #000000">};</span></div> <div>    <span style="color: #000000">}</span></div> <div><span style="color: #000000">});</span></div> </div><p>That would produce the following output.</p> <div class="code lang-javascript"> <div><span style="color: #000000">expect</span><span style="color: #000000">(</span><span style="color: #a71d5d">new</span> Person<span style="color: #000000">(</span><span style="color: #df5000">'John Doe'</span><span style="color: #000000">,</span> <span style="color: #0086b3">42</span><span style="color: #000000">),</span> <span style="color: #df5000">'to equal'</span><span style="color: #000000">,</span> <span style="color: #a71d5d">new</span> Person<span style="color: #000000">(</span><span style="color: #df5000">'Jane Doe'</span><span style="color: #000000">,</span> <span style="color: #0086b3">24</span><span style="color: #000000">));</span></div> </div><div class="output"> <div><span style="color: red; font-weight: bold">expected</span> new Person(<span style="color: #df5000">'John Doe'</span>, <span style="color: #0086b3">42</span>) <span style="color: red; font-weight: bold">to equal</span> new Person(<span style="color: #df5000">'Jane Doe'</span>, <span style="color: #0086b3">24</span>)</div> <div> </div> <div>new Person(</div> <div>  <span style="color: #df5000">'John Doe'</span>, <div style="display: inline-block; vertical-align: top"> <div><span style="color: red; font-weight: bold">//</span></div> <div><span style="color: red; font-weight: bold">//</span></div> <div><span style="color: red; font-weight: bold">//</span></div> </div> <div style="display: inline-block; vertical-align: top"> <div><span style="color: red; font-weight: bold">should be </span><span style="color: #df5000">'Jane Doe'</span></div> <div><div style="display: inline-block; vertical-align: top"> <div><span style="color: red">-</span></div> </div><div style="display: inline-block; vertical-align: top"> <div><span style="background-color: red; color: white">John</span><span style="color: red"> Doe</span></div> </div></div> <div><div style="display: inline-block; vertical-align: top"> <div><span style="color: green">+</span></div> </div><div style="display: inline-block; vertical-align: top"> <div><span style="background-color: green; color: white">Jane</span><span style="color: green"> Doe</span></div> </div></div> </div></div> <div>  <span style="color: #0086b3">42</span></div> <div>)</div> </div><p>This is a rather complicated example and I won't go though the details, but I would like to comment on the <code>inline</code> flag. When we diff objects against each other, the values of the keys will be diffed against each other. That means diffs are inserted into the containing structure. You can control this behavior using the <code>inline</code> flag. If the child diff is inline, it means that it will be appended directly into the parent; otherwise the diff will be inserted in an annotation block. The outputs below shows the contrast between setting the <code>Person</code> diff to inline or not.</p> <div class="code lang-javascript"> <div>inlineDiff <span style="color: #a71d5d">=</span> <span style="color: #0086b3">true</span><span style="color: #000000">;</span></div> <div><span style="color: #000000">expect</span><span style="color: #000000">(</span></div> <div>  <span style="color: #000000">{</span><span style="color: #df5000">'John Doe'</span><span style="color: #000000">:</span> <span style="color: #a71d5d">new</span> Person<span style="color: #000000">(</span><span style="color: #df5000">'John Doe'</span><span style="color: #000000">,</span> <span style="color: #0086b3">42</span><span style="color: #000000">),</span> <span style="color: #df5000">'Jane Doe'</span><span style="color: #000000">:</span> <span style="color: #a71d5d">new</span> Person<span style="color: #000000">(</span><span style="color: #df5000">'Janie Doe'</span><span style="color: #000000">,</span> <span style="color: #0086b3">24</span><span style="color: #000000">)},</span></div> <div>  <span style="color: #df5000">'to equal'</span><span style="color: #000000">,</span></div> <div>  <span style="color: #000000">{</span><span style="color: #df5000">'John Doe'</span><span style="color: #000000">:</span> <span style="color: #a71d5d">new</span> Person<span style="color: #000000">(</span><span style="color: #df5000">'John Doe'</span><span style="color: #000000">,</span> <span style="color: #0086b3">42</span><span style="color: #000000">),</span> <span style="color: #df5000">'Jane Doe'</span><span style="color: #000000">:</span> <span style="color: #a71d5d">new</span> Person<span style="color: #000000">(</span><span style="color: #df5000">'Jane Doe'</span><span style="color: #000000">,</span> <span style="color: #0086b3">24</span><span style="color: #000000">)}</span></div> <div><span style="color: #000000">);</span></div> </div><div class="output"> <div><span style="color: red; font-weight: bold">expected</span></div> <div>{</div> <div>  <div style="display: inline-block; vertical-align: top"> <div><span style="color: #df5000">'John Doe'</span>: new Person(<span style="color: #df5000">'John Doe'</span>, <span style="color: #0086b3">42</span>),</div> <div><span style="color: #df5000">'Jane Doe'</span>: new Person(<span sty