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"articleBody":"This post is part of a series where I'm hoping to prove to myself that building a dynamic website with NodeJS is much more fun than using a CMS platform. See the first post for an explanation of why\n\nThe code can be found on GitHub\n\nPrevious Post\n\n\n A promise represents the eventual result of an asynchronous operation.\n\n\nThe basic idea is that you can swap in a promise where you would normally pass in a callback.\n\nThe primary interaction is that you call a method which returns a promise which will eventually return a result (it can immediately return the result if it's available) and you chain a call to .then() onto that method call.\n\nThe call to then is equivalent to passing in the callback function.\n\nClear as mud?\n\n\n\nThere's (much) more at the Promises specification website.\n\nBluebird\nThis is JavaScript so there are a bazillion npm packages that could be used to switch the project's code to using promises. A (relatively small) bit of googling research suggested that the Bluebird library was a good bet.\n\nIn their words:\n\n\n Bluebird is a fully featured promise library with focus on innovative features and performance\n\n\nBefore\nHere's the code from the previous Post which shows the smelly, arrow anti-pattern\n\nvar bcrypt = require('bcrypt');\nvar SALT_WORK_FACTOR = 10;\n\nmodule.exports = function(db) {\n return {\n create: function(username, password, callback) {\n bcrypt.genSalt(SALT_WORK_FACTOR, function(err, salt) {\n if (err) {\n callback(err);\n return;\n }\n bcrypt.hash(password, salt, function(err, hash) {\n if (err) {\n callback(err);\n return;\n }\n db.users.save({\n username:username,\n password:hash\n }, function(err, result) {\n if(err) {\n callback(err.err);\n } else {\n callback('user created');\n }\n });\n });\n });\n }\n };\n};\n\n\nThis took a bit of faff to translate to promises almost entirely as a result of this being the first ever promises code I've written and I didn't RTFM.\n\nI did have this code covered by tests so I could leave mocha running in the background and poke the code with a stick (Yay TDD!)\n\nAfter\nThe first pass at implementing promises generated:\n\nvar SALT_WORK_FACTOR = 10;\n\nvar bcrypt = require('bcrypt');\nvar Promise = require('bluebird');\n\nvar genSalt = Promise.promisify(bcrypt.genSalt);\nvar genHash = Promise.promisify(bcrypt.hash);\n\nmodule.exports = function(db) {\n var users = Promise.promisifyAll(db.users);\n\n return {\n create: function(username, password, callback) {\n genSalt(SALT_WORK_FACTOR).then(function(salt) {\n\t return genHash(password, salt);\n\t }).then(function(hash) {\n return users.saveAsync({\n username:username,\n password:hash\n });\n }).then(function() {\n callback('user created');\n }).error(function (e) {\n callback(e.message);\n });\n }\n };\n};\n\n\nAll tests still pass at this point and there's fewer levels of arrow to wade through but it still feels a bit pointy and not massively clear so…\n\nvar SALT_WORK_FACTOR = 10;\n\nvar bcrypt = require('bcrypt');\nvar Promise = require('bluebird');\n\nvar genSalt = Promise.promisify(bcrypt.genSalt);\nvar genHash = Promise.promisify(bcrypt.hash);\n\nmodule.exports = function(db) {\n var users = Promise.promisifyAll(db.users);\n\n return {\n create: function(username, password, callback) {\n var hashPassword = function() {\n return genSalt(SALT_WORK_FACTOR).then(function(salt) {\n return genHash(password, salt);\n });\n };\n\n var persistUser = function(hashedPassword) {\n return users.saveAsync({\n username:username,\n password:hashedPassword\n });\n };\n\n hashPassword()\n .then(persistUser)\n .then(function() {\n callback('user created');\n }).error(function (e) {\n callback(e.message);\n });\n }\n };\n};\n\n\nskipping over the setup code you can get to the meat of the module\n\nhashPassword()\n.then(persistUser)\n.then(function() {\n callback('user created');\n}).error(function (e) {\n callback(e.message);\n});\n\n\nWhich is a huge amount clearer than the starting point! I do like a method to be a sentence! 'Hash password then persist user'!\n\nA very high count of exclamation marks in this post but that was much easier and more fun than I anticipated - winner!\n\nAt this point I either need to pass through the code to implement promises more widely… or I could choose to leave everything as it is and improve each code file as it's touched.\n\nAs it is it's nearly midnight and my alarm goes off at 5:50am so…\n"
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<div class="date">Sun May 18 2014</div>
<h1 class="title leading-10 pt-2 mb-0 mt-1">Websites != CMS Platform - Promises</h1>
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<p>This post is part of a series where I'm hoping to prove to myself that building a dynamic website with NodeJS is much more fun than using a CMS platform. <a href="/2014/02/websites-cms.html">See the first post for an explanation of why</a></p>
<p>The code can be found on <a href="https://github.com/pauldambra/omniclopse">GitHub</a></p>
<p><a href="/websites-CMS-platform-logging-in.html">Previous Post</a></p>
<blockquote>
<p>A promise represents the eventual result of an asynchronous operation.</p>
</blockquote>
<p>The basic idea is that you can swap in a promise where you would normally pass in a callback.</p>
<p>The primary interaction is that you call a method which returns a promise which will eventually return a result (it <em>can</em> immediately return the result if it's available) and you chain a call to <code class="language-plaintext highlighter-rouge">.then()</code> onto that method call.</p>
<p>The call to then is equivalent to passing in the callback function.</p>
<p>Clear as mud?</p>
<!--more-->
<p>There's (much) more at the <a href="http://promisesaplus.com/">Promises specification website</a>.</p>
<h1 id="bluebird">Bluebird</h1>
<p>This is JavaScript so there are a bazillion npm packages that could be used to switch the project's code to using promises. A (relatively small) bit of <del>googling</del> research suggested that the <a href="https://www.npmjs.org/package/bluebird">Bluebird</a> library was a good bet.</p>
<p>In their words:</p>
<blockquote>
<p>Bluebird is a fully featured promise library with focus on innovative features and performance</p>
</blockquote>
<h1 id="before">Before</h1>
<p>Here's the code from the <a href="/websites-CMS-platform-logging-in.html">previous Post</a> which shows the smelly, <a href="http://c2.com/cgi/wiki?ArrowAntiPattern">arrow anti-pattern</a></p>
<div class="language-js highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="kd">var</span> <span class="nx">bcrypt</span> <span class="o">=</span> <span class="nf">require</span><span class="p">(</span><span class="dl">'</span><span class="s1">bcrypt</span><span class="dl">'</span><span class="p">);</span>
<span class="kd">var</span> <span class="nx">SALT_WORK_FACTOR</span> <span class="o">=</span> <span class="mi">10</span><span class="p">;</span>
<span class="nx">module</span><span class="p">.</span><span class="nx">exports</span> <span class="o">=</span> <span class="kd">function</span><span class="p">(</span><span class="nx">db</span><span class="p">)</span> <span class="p">{</span>
<span class="k">return</span> <span class="p">{</span>
<span class="na">create</span><span class="p">:</span> <span class="kd">function</span><span class="p">(</span><span class="nx">username</span><span class="p">,</span> <span class="nx">password</span><span class="p">,</span> <span class="nx">callback</span><span class="p">)</span> <span class="p">{</span>
<span class="nx">bcrypt</span><span class="p">.</span><span class="nf">genSalt</span><span class="p">(</span><span class="nx">SALT_WORK_FACTOR</span><span class="p">,</span> <span class="kd">function</span><span class="p">(</span><span class="nx">err</span><span class="p">,</span> <span class="nx">salt</span><span class="p">)</span> <span class="p">{</span>
<span class="k">if </span><span class="p">(</span><span class="nx">err</span><span class="p">)</span> <span class="p">{</span>
<span class="nf">callback</span><span class="p">(</span><span class="nx">err</span><span class="p">);</span>
<span class="k">return</span><span class="p">;</span>
<span class="p">}</span>
<span class="nx">bcrypt</span><span class="p">.</span><span class="nf">hash</span><span class="p">(</span><span class="nx">password</span><span class="p">,</span> <span class="nx">salt</span><span class="p">,</span> <span class="kd">function</span><span class="p">(</span><span class="nx">err</span><span class="p">,</span> <span class="nx">hash</span><span class="p">)</span> <span class="p">{</span>
<span class="k">if </span><span class="p">(</span><span class="nx">err</span><span class="p">)</span> <span class="p">{</span>
<span class="nf">callback</span><span class="p">(</span><span class="nx">err</span><span class="p">);</span>
<span class="k">return</span><span class="p">;</span>
<span class="p">}</span>
<span class="nx">db</span><span class="p">.</span><span class="nx">users</span><span class="p">.</span><span class="nf">save</span><span class="p">({</span>
<span class="na">username</span><span class="p">:</span><span class="nx">username</span><span class="p">,</span>
<span class="na">password</span><span class="p">:</span><span class="nx">hash</span>
<span class="p">},</span> <span class="kd">function</span><span class="p">(</span><span class="nx">err</span><span class="p">,</span> <span class="nx">result</span><span class="p">)</span> <span class="p">{</span>
<span class="k">if</span><span class="p">(</span><span class="nx">err</span><span class="p">)</span> <span class="p">{</span>
<span class="nf">callback</span><span class="p">(</span><span class="nx">err</span><span class="p">.</span><span class="nx">err</span><span class="p">);</span>
<span class="p">}</span> <span class="k">else</span> <span class="p">{</span>
<span class="nf">callback</span><span class="p">(</span><span class="dl">'</span><span class="s1">user created</span><span class="dl">'</span><span class="p">);</span>
<span class="p">}</span>
<span class="p">});</span>
<span class="p">});</span>
<span class="p">});</span>
<span class="p">}</span>
<span class="p">};</span>
<span class="p">};</span>
</code></pre></div></div>
<p>This took a bit of faff to translate to promises almost entirely as a result of this being the first ever promises code I've written and I didn't RTFM.</p>
<p>I did have this code covered by tests so I could leave mocha running in the background and poke the code with a stick (Yay TDD!)</p>
<h1 id="after">After</h1>
<p>The first pass at implementing promises generated:</p>
<div class="language-js highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="kd">var</span> <span class="nx">SALT_WORK_FACTOR</span> <span class="o">=</span> <span class="mi">10</span><span class="p">;</span>
<span class="kd">var</span> <span class="nx">bcrypt</span> <span class="o">=</span> <span class="nf">require</span><span class="p">(</span><span class="dl">'</span><span class="s1">bcrypt</span><span class="dl">'</span><span class="p">);</span>
<span class="kd">var</span> <span class="nb">Promise</span> <span class="o">=</span> <span class="nf">require</span><span class="p">(</span><span class="dl">'</span><span class="s1">bluebird</span><span class="dl">'</span><span class="p">);</span>
<span class="kd">var</span> <span class="nx">genSalt</span> <span class="o">=</span> <span class="nb">Promise</span><span class="p">.</span><span class="nf">promisify</span><span class="p">(</span><span class="nx">bcrypt</span><span class="p">.</span><span class="nx">genSalt</span><span class="p">);</span>
<span class="kd">var</span> <span class="nx">genHash</span> <span class="o">=</span> <span class="nb">Promise</span><span class="p">.</span><span class="nf">promisify</span><span class="p">(</span><span class="nx">bcrypt</span><span class="p">.</span><span class="nx">hash</span><span class="p">);</span>
<span class="nx">module</span><span class="p">.</span><span class="nx">exports</span> <span class="o">=</span> <span class="kd">function</span><span class="p">(</span><span class="nx">db</span><span class="p">)</span> <span class="p">{</span>
<span class="kd">var</span> <span class="nx">users</span> <span class="o">=</span> <span class="nb">Promise</span><span class="p">.</span><span class="nf">promisifyAll</span><span class="p">(</span><span class="nx">db</span><span class="p">.</span><span class="nx">users</span><span class="p">);</span>
<span class="k">return</span> <span class="p">{</span>
<span class="na">create</span><span class="p">:</span> <span class="kd">function</span><span class="p">(</span><span class="nx">username</span><span class="p">,</span> <span class="nx">password</span><span class="p">,</span> <span class="nx">callback</span><span class="p">)</span> <span class="p">{</span>
<span class="nf">genSalt</span><span class="p">(</span><span class="nx">SALT_WORK_FACTOR</span><span class="p">).</span><span class="nf">then</span><span class="p">(</span><span class="kd">function</span><span class="p">(</span><span class="nx">salt</span><span class="p">)</span> <span class="p">{</span>
<span class="k">return</span> <span class="nf">genHash</span><span class="p">(</span><span class="nx">password</span><span class="p">,</span> <span class="nx">salt</span><span class="p">);</span>
<span class="p">}).</span><span class="nf">then</span><span class="p">(</span><span class="kd">function</span><span class="p">(</span><span class="nx">hash</span><span class="p">)</span> <span class="p">{</span>
<span class="k">return</span> <span class="nx">users</span><span class="p">.</span><span class="nf">saveAsync</span><span class="p">({</span>
<span class="na">username</span><span class="p">:</span><span class="nx">username</span><span class="p">,</span>
<span class="na">password</span><span class="p">:</span><span class="nx">hash</span>
<span class="p">});</span>
<span class="p">}).</span><span class="nf">then</span><span class="p">(</span><span class="kd">function</span><span class="p">()</span> <span class="p">{</span>
<span class="nf">callback</span><span class="p">(</span><span class="dl">'</span><span class="s1">user created</span><span class="dl">'</span><span class="p">);</span>
<span class="p">}).</span><span class="nf">error</span><span class="p">(</span><span class="nf">function </span><span class="p">(</span><span class="nx">e</span><span class="p">)</span> <span class="p">{</span>
<span class="nf">callback</span><span class="p">(</span><span class="nx">e</span><span class="p">.</span><span class="nx">message</span><span class="p">);</span>
<span class="p">});</span>
<span class="p">}</span>
<span class="p">};</span>
<span class="p">};</span>
</code></pre></div></div>
<p>All tests still pass at this point and there's fewer levels of arrow to wade through but it still feels a bit pointy and not massively clear so…</p>
<div class="language-js highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="kd">var</span> <span class="nx">SALT_WORK_FACTOR</span> <span class="o">=</span> <span class="mi">10</span><span class="p">;</span>
<span class="kd">var</span> <span class="nx">bcrypt</span> <span class="o">=</span> <span class="nf">require</span><span class="p">(</span><span class="dl">'</span><span class="s1">bcrypt</span><span class="dl">'</span><span class="p">);</span>
<span class="kd">var</span> <span class="nb">Promise</span> <span class="o">=</span> <span class="nf">require</span><span class="p">(</span><span class="dl">'</span><span class="s1">bluebird</span><span class="dl">'</span><span class="p">);</span>
<span class="kd">var</span> <span class="nx">genSalt</span> <span class="o">=</span> <span class="nb">Promise</span><span class="p">.</span><span class="nf">promisify</span><span class="p">(</span><span class="nx">bcrypt</span><span class="p">.</span><span class="nx">genSalt</span><span class="p">);</span>
<span class="kd">var</span> <span class="nx">genHash</span> <span class="o">=</span> <span class="nb">Promise</span><span class="p">.</span><span class="nf">promisify</span><span class="p">(</span><span class="nx">bcrypt</span><span class="p">.</span><span class="nx">hash</span><span class="p">);</span>
<span class="nx">module</span><span class="p">.</span><span class="nx">exports</span> <span class="o">=</span> <span class="kd">function</span><span class="p">(</span><span class="nx">db</span><span class="p">)</span> <span class="p">{</span>
<span class="kd">var</span> <span class="nx">users</span> <span class="o">=</span> <span class="nb">Promise</span><span class="p">.</span><span class="nf">promisifyAll</span><span class="p">(</span><span class="nx">db</span><span class="p">.</span><span class="nx">users</span><span class="p">);</span>
<span class="k">return</span> <span class="p">{</span>
<span class="na">create</span><span class="p">:</span> <span class="kd">function</span><span class="p">(</span><span class="nx">username</span><span class="p">,</span> <span class="nx">password</span><span class="p">,</span> <span class="nx">callback</span><span class="p">)</span> <span class="p">{</span>
<span class="kd">var</span> <span class="nx">hashPassword</span> <span class="o">=</span> <span class="kd">function</span><span class="p">()</span> <span class="p">{</span>
<span class="k">return</span> <span class="nf">genSalt</span><span class="p">(</span><span class="nx">SALT_WORK_FACTOR</span><span class="p">).</span><span class="nf">then</span><span class="p">(</span><span class="kd">function</span><span class="p">(</span><span class="nx">salt</span><span class="p">)</span> <span class="p">{</span>
<span class="k">return</span> <span class="nf">genHash</span><span class="p">(</span><span class="nx">password</span><span class="p">,</span> <span class="nx">salt</span><span class="p">);</span>
<span class="p">});</span>
<span class="p">};</span>
<span class="kd">var</span> <span class="nx">persistUser</span> <span class="o">=</span> <span class="kd">function</span><span class="p">(</span><span class="nx">hashedPassword</span><span class="p">)</span> <span class="p">{</span>
<span class="k">return</span> <span class="nx">users</span><span class="p">.</span><span class="nf">saveAsync</span><span class="p">({</span>
<span class="na">username</span><span class="p">:</span><span class="nx">username</span><span class="p">,</span>
<span class="na">password</span><span class="p">:</span><span class="nx">hashedPassword</span>
<span class="p">});</span>
<span class="p">};</span>
<span class="nf">hashPassword</span><span class="p">()</span>
<span class="p">.</span><span class="nf">then</span><span class="p">(</span><span class="nx">persistUser</span><span class="p">)</span>
<span class="p">.</span><span class="nf">then</span><span class="p">(</span><span class="kd">function</span><span class="p">()</span> <span class="p">{</span>
<span class="nf">callback</span><span class="p">(</span><span class="dl">'</span><span class="s1">user created</span><span class="dl">'</span><span class="p">);</span>
<span class="p">}).</span><span class="nf">error</span><span class="p">(</span><span class="nf">function </span><span class="p">(</span><span class="nx">e</span><span class="p">)</span> <span class="p">{</span>
<span class="nf">callback</span><span class="p">(</span><span class="nx">e</span><span class="p">.</span><span class="nx">message</span><span class="p">);</span>
<span class="p">});</span>
<span class="p">}</span>
<span class="p">};</span>
<span class="p">};</span>
</code></pre></div></div>
<p>skipping over the setup code you can get to the meat of the module</p>
<div class="language-js highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="nf">hashPassword</span><span class="p">()</span>
<span class="p">.</span><span class="nf">then</span><span class="p">(</span><span class="nx">persistUser</span><span class="p">)</span>
<span class="p">.</span><span class="nf">then</span><span class="p">(</span><span class="kd">function</span><span class="p">()</span> <span class="p">{</span>
<span class="nf">callback</span><span class="p">(</span><span class="dl">'</span><span class="s1">user created</span><span class="dl">'</span><span class="p">);</span>
<span class="p">}).</span><span class="nf">error</span><span class="p">(</span><span class="nf">function </span><span class="p">(</span><span class="nx">e</span><span class="p">)</span> <span class="p">{</span>
<span class="nf">callback</span><span class="p">(</span><span class="nx">e</span><span class="p">.</span><span class="nx">message</span><span class="p">);</span>
<span class="p">});</span>
</code></pre></div></div>
<p>Which is a huge amount clearer than the starting point! I do like a method to be a sentence! 'Hash password then persist user'!</p>
<p>A very high count of exclamation marks in this post but that was much easier and more fun than I anticipated - winner!</p>
<p>At this point I either need to pass through the code to implement promises more widely… or I could choose to leave everything as it is and improve each code file as it's touched.</p>
<p>As it is it's nearly midnight and my alarm goes off at 5:50am so…</p>
</div>
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