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Promises, when used correctly, produce easy-to-read code that is easier to reason about, and thus easier to debug than callbacks. There is no need to set up conventions regarding, for example, error handling since they are already part of the specification.

<span class="hljs-function"><span class="hljs-keyword">function</span> <span class="hljs-title">dieToss</span><span class="hljs-params">()</span> {</span>
  <span class="hljs-keyword">return</span> <span class="hljs-transposed_variable">Math.</span><span class="hljs-built_in">floor</span>(<span class="hljs-transposed_variable">Math.</span>random() * <span class="hljs-number">6</span>) + <span class="hljs-number">1</span>;
}

<span class="hljs-transposed_variable">console.</span><span class="hljs-built_in">log</span>(<span class="hljs-string">'1'</span>);
var promise = new <span class="hljs-transposed_variable">RSVP.</span>Promise(<span class="hljs-function"><span class="hljs-keyword">function</span><span class="hljs-params">(fulfill, reject)</span> {</span>
  var n = dieToss();
  <span class="hljs-keyword">if</span> (n === <span class="hljs-number">6</span>) <span class="hljs-cell">{
    fulfill(n);
  }</span> <span class="hljs-keyword">else</span> <span class="hljs-cell">{
    reject(n);
  }</span>
  <span class="hljs-transposed_variable">console.</span><span class="hljs-built_in">log</span>(<span class="hljs-string">'2'</span>);
});

<span class="hljs-transposed_variable">promise.</span>then(<span class="hljs-function"><span class="hljs-keyword">function</span><span class="hljs-params">(toss)</span> {</span>
  <span class="hljs-transposed_variable">console.</span><span class="hljs-built_in">log</span>(<span class="hljs-string">'Yay, threw a '</span> + toss + <span class="hljs-string">'.'</span>);  
}, <span class="hljs-function"><span class="hljs-keyword">function</span><span class="hljs-params">(toss)</span> {</span>
  <span class="hljs-transposed_variable">console.</span><span class="hljs-built_in">log</span>(<span class="hljs-string">'Oh, noes, threw a '</span> + toss + <span class="hljs-string">'.'</span>);  
});
<span class="hljs-transposed_variable">console.</span><span class="hljs-built_in">log</span>(<span class="hljs-string">'3'</span>);