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copied!<blockquote> <p>See also <a href="https://stackoverflow.com/q/20883421/1048572">Sorting in JavaScript: Should every compare function have a "return 0" statement?</a></p> </blockquote> <hr> <pre><code>if (a.to != b.from) return 1; if (a.to == b.from) return -1; </code></pre> <p>That's not a consistent compare function (violating the reflexivity, i.e. <code>compare(x, x) == 0</code>, for example). What do you expect it to do?</p> <p>Citing the <a href="http://es5.github.com/#x15.4.4.11" rel="nofollow noreferrer">ES5.1 spec on <code>sort</code></a>:</p> <blockquote> <p>If <code>comparefn</code> is […] not a consistent comparison function for the elements of this array, the behaviour of sort is implementation-defined.</p> <p>A function <code>comparefn</code> is a consistent comparison function for a set of values <code>S</code> if all of the requirements below are met for all values <code>a</code>, <code>b</code>, and <code>c</code> (possibly the same value) in the set <code>S</code>: The notation <code>a <CF b</code> means <code>comparefn(a,b) < 0</code>; <code>a =CF b</code> means <code>comparefn(a,b) = 0</code> (of either sign); and <code>a >CF b</code> means <code>comparefn(a,b) > 0</code>.</p> <p>Calling <code>comparefn(a,b)</code> always returns the same value <code>v</code> when given a specific pair of values <code>a</code> and <code>b</code> as its two arguments. Furthermore, <code>Type(v)</code> is Number, and <code>v</code> is not <code>NaN</code>. Note that this implies that exactly one of <code>a <CF b</code>, <code>a =CF b</code>, and <code>a >CF b</code> will be true for a given pair of <code>a</code> and <code>b</code>.</p> <ul> <li>Calling <code>comparefn(a,b)</code> does not modify the this object.</li> <li><code>a =CF a</code> (reflexivity)</li> <li>If <code>a =CF b</code>, then <code>b =CF a</code> (symmetry)</li> <li>If <code>a =CF b</code> and <code>b =CF c</code>, then <code>a =CF c</code> (transitivity of <code>=CF</code>)</li> <li>If <code>a <CF b</code> and <code>b <CF c</code>, then <code>a <CF c</code> (transitivity of <code><CF</code>)</li> <li>If <code>a >CF b</code> and <code>b >CF c</code>, then <code>a >CF c</code> (transitivity of <code>>CF</code>)</li> </ul> <p>NOTE: The above conditions are necessary and sufficient to ensure that <code>comparefn</code> divides the set <code>S</code> into equivalence classes and that these equivalence classes are totally ordered.</p> </blockquote>

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