Javascript is Wierd.

wierd.js

[] + []
// returns an empty string, ''

[] + [0]
// returns a string, '0'

[0] + [0]
// returns a string, '00'

[0,0] + [0]
// returns a string, '00,0'

[] + {}
// returns either a string of '[obejct Object]', or [object Object]

{} + []
// returns 0

{} + {};
// returns NaN ( Not a number. )

++[[]][+[]]+[+[]];
// Returns string '10'