Equality =
[1, 2, 3] == [1, 2, 3]
is described under The Abstract Equality Comparison Algorithm, which basically says
(if x or y are primitives, compare them, otherwise...)
Return true if x and y refer to the same object. Otherwise, return false.
Since different object literals always represent different objects, even if the content is the same, the above comparison fails.
Relational operators < >
Relative comparisons are different from equality. When you use < or >, arrays are compared as strings.
[1, 2, 4] < [1, 2, 5]
The Abstract Relational Comparison Algorithm converts both operands to primitives. If an operand is an object, ToPrimitive calls [[DefaultValue]] which in turn is the same as obj.valueOf().toString(). Since valueOf of an object is the object itself, the whole thing boils down to
"1,2,4" < "1,2,5"
A common assumption that arrays are compared element-wise is not true:
[10,1,3] < [101,5] // false
Note that valueOf can be overridden to affect the behavior of relational operators:
> a = [1,2,3]
[1, 2, 3]
> a < [1,2,4]
true
> a.valueOf = function() { return 'zzz' }
function () { return 'zzz' }
> a < [1,2,4]
false
