undefined
[object Object]
undefined
0
true
's' + undefined => s
undefined + 's' => s
0 + undefined => 0
undefined + 0 => 0
'undefined' == undefined => false
undefined == 'undefined' => false
0 == undefined => false
undefined == 0 => false
1 == undefined => false
undefined == 1 => false
'undefined' < undefined => 
undefined < 'undefined' => 
0 < undefined => false
undefined < 0 => false
1 < undefined => false
undefined < 1 => true
'undefined' <= undefined => true
undefined <= 'undefined' => true
0 <= undefined => true
undefined <= 0 => true
1 <= undefined => false
undefined <= 1 => true
'undefined' > undefined => 
undefined > 'undefined' => 
0 > undefined => false
undefined > 0 => false
1 > undefined => true
undefined > 1 => false
'undefined' >= undefined => true
undefined >= 'undefined' => true
0 >= undefined => true
undefined >= 0 => true
1 >= undefined => true
undefined >= 1 => false
