Kata

As of now, random tests have random inputs, but not random expected values. That means they're predictable, can be hardcoded, and are insufficient as random tests.

That said, hardcoding this kata hardly seems worth it; it's less work to just solve it.

@brice: In which comment do you want to add a (which?) message ?

Done.

Ok, modified too.

Believe it or not, there is a relatively simple explanation, and it isn't that Javascript treats them differently. It's because of Array.prototype.toString, and how that string is subsequently coerced to a number.

When necessary to perform comparisons between an object and a primitive, the object is coerced to a string using its toString method:

[1,2] > 0 becomes "1,2" > 0

Now, if one side of a comparison is a number (or boolean), the other side is coerced to a number as well; otherwise, they're compared as strings. So:

"1,2" > 0 becomes NaN > 0

"1,2" > "0" isn't changed, because neither side is a number

If you change Array.prototype.toString, then an array such as [1,2] can become any string you want it to become. E.g.

// default behavior: join on ','
[1,2] == "1,2";           // true: "1,2" == "1,2" is true
[1,2] == NaN;             // false: NaN == NaN is false
[1,2] > 0;                // false: NaN > 0 is false

// new behavior: join on '.'
Array.prototype.toString = function () { return this.join('.'); };
[1,2] == "1.2";           // true: "1.2" == "1.2" is true
[1,2] == 1.2;             // true: 1.2 == 1.2 is true
[1,2] > 0;                // true: 1.2 > 0 is true

// new behavior: join on 'e' (coercing "1e2" to a number yields 100)
Array.prototype.toString = function () { return this.join('e'); };
[1,2] == "1e2";           // true: "1e2" == "1e2" is true
[1,2] == 100;             // true: 100 == 100 is true
[1,2] > 0;                // true: 100 > 0 is true

// new behavior: join on 'x' (coercing "0x10" to a number yields 16)
Array.prototype.toString = function () { return this.join('x'); };
[0,10] == "0x10";         // true: "0x10" == "0x10" is true
[0,10] == 16;             // true: 16 == 16 is true
[0,10] > 0;               // true: 16 > 0 is true

// new behavior: join on ''
Array.prototype.toString = function () { return this.join(''); };
[1,2,3,4,5] == "12345";   // true: "12345" == "12345" is true
[1,2,3,4,5] == 12345;     // true: 12345 == 12345 is true
[1,2,3,4,5] > 0;          // true: 12345 > 0 is true