Javascript Ie 9: Custom Sort Function

In IE 9, if I type this in the console: [1, 4, 2, 3].sort(function (a, b) { return a < b; }); The resulting array is: [1, 4, 2, 3]. If I do this in FF/Chrome, I get it, reverse

Solution 1:

Maybe because the function is supposed to return -1 if a is smaller, 0 if they are equal, and 1 if a is larger (or vice versa if you want reverse order). Edit: In fact, it must be zero, a positive or negative number (as @pimvdb pointed out, and that's what I make use of in the example below). Your function will never return -1 though and that might create problems.

Consider 1 and 3. Your function returns 1 for 1 < 3, which is ok, but returns 0 for 3 < 1. In one case the number are different, in the other you are saying that they are equal.

That FF/Chrome sort it in reverse order might be due to the sorting algorithm they are using.

Try:

[1, 4, 2, 3].sort(function (a, b) { return b - a; });

Update: To substantiate this, we can have a look at the specification, Section 15.4.4.11 Array.prototype.sort(comparefn), where the properties are given which have to be fulfilled by a comparison function:

A function comparefn is a consistent comparison function for a set of values S if all of the requirements below are met for all values a, b, and c (possibly the same value) in the set S: The notation a <_CFb means comparefn(a,b) < 0; a =_CFb means comparefn(a,b) = 0 (of either sign); and a >_CFb means comparefn(a,b) > 0.

• Calling comparefn(a,b) always returns the same value v when given a specific pair of values a and b as its two arguments. Furthermore, Type(v) is Number, and v is not NaN. Note that this implies that exactly one of a <_CFb, a =_CFb, and a >_CFb will be true for a given pair of a and b.
• Calling comparefn(a,b) does not modify the this object.
• a =_CFa (reflexivity)
• If a =_CFb, then b =_CFa (symmetry)
• If a =_CFb and b =_CFc, then a =_CFc (transitivity of =_CF)
• If a <_CFb and b <_CFc, then a <_CFc (transitivity of <_CF)
• If a >_CFb and b >_CFc, then a >_CFc (transitivity of >_CF)

NOTE The above conditions are necessary and sufficient to ensure that comparefn divides the set S into equivalence classes and that these equivalence classes are totally ordered.