How is the JavaScript sort function implemented?

Question

Let's look at an example first.

var everything = [4,'Red', '$200', 'white', 7.4, 12, true, 0.3, false]; console.log(everything.sort(function(a, b) {return a - b;})); // [4, "Red", "$200", "white", false, 0.3, true, 7.4, 12] 

I think this is strange, even when I know Number("Red") , Number("$200") and Number("white") , all give NaN when compared.

Why 4 in the first result? I assume this has something to do with the implementation of Array.prototype.sort , so how can I see its implementation?

Answer 1

Specification

According to ECMAScript 5 - Section 15.4.4.11 ,

If comparefn is not undefined and is not a sequential comparison function for the elements of this array (see below), the sorting behavior is determined by the implementation ,

[...]

The comparefn function is a sequential comparison function for a set of values ​​of S if all the requirements below are satisfied for all values ​​of a, b, and c (possibly the same value) in the set S [...]

• The call comparefn (a, b) always returns the same value of v when it is given a specific pair of values ​​a and b as two arguments. In addition, Type (v) is Number, and v is not NaN . [...]

That is, if the return value of the comparison function is NaN, then the behavior of the call to sort is determined by "implementation".

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On practice

Google Chrome and NodeJS (V8 Engine), as well as Opera (Futhark / Carakan) are returned:

 [4, "Red", "$200", "white", false, 0.3, true, 7.4, 12] 

Firefox (SpiderMonkey) returns:

 [false, 0.3, true, 4, "Red", "$200", "white", 7.4, 12] 

Internet Explorer returns:

 ["Red", "$200", false, 0.3, true, 4, "white", 7.4, 12]