wtf.js

/* VT100 terminal reset (<ESC>c) */

console.log('\033c');

/* numbers comparations */

> '2' == 2
true

> '2' === 2
false

> [2] == 2
true

> [] + []
''

> [] == []
false

> typeof []
'object'

> [] == ![]
true

> +[] == +![]
true

/* null comparation */

> 0 > null
false

> 0 >= null
true

> 0 == null
false

> 0 <= null
true

> 0 < null
false

> typeof null
'object'

> null instanceof Object
false

/* checking array type */

> {}.toString.call([])
'[object Array]'

> function FooBar() {}
undefined

> {}.toString.call(new FooBar)
'[object Object]'

> (new FooBar).constructor == Foo
false

> [] instanceof Array
true

> Array.isArray([])
true

/* math */

> 999999999999999
999999999999999

> 9999999999999999
10000000000000000

> -9999999999999999
-10000000000000000

> 0.1 + 0.2 == 0.3
false

> 0.1 + 0.2
0.30000000000000004

> 3 > 2 > 1
false

> 3 > 2 >= 1
true

> '2' + 1
'21'

> '2' - 1
1

> '2' - -1
3

> 1/0
Infinity

> typeof Infinity
'number'

> 0 === -0
true

> 1/0
Infinity

> 1/-0
-Infinity

> Infinity == -Infinity
false

Number.MAX_VALUE
1.7976931348623157e+308

> 0 - 1
-1

> Number.MIN_VALUE < 0
false

> Number.MIN_VALUE
5e-324>

> Math.max(1,2,3)
3

> Math.min(1,2,3)
1

> Math.max() > Math.min()
false

> Math.max()
-Infinity

> Math.min()
Infinity

/* string */

> 'wtf' instanceof String
false

> typeof 'wtf'
'string'

> typeof String('wtf')
'string'

> String('wtf') === 'wtf'
true

> String('wtf') === new String('wtf')
false

> String('wtf') == new String('wtf')
true

> new String('wtf')
{ '0': 'w',
  '1': 't',
  '2': 'f' }

> new String('wtf').toString()
'wtf'

> 'wft' + 1
'wft1'

> 'wft' - 1
NaN

/* NaN */

> typeof NaN
'number'

> typeof 1138
'number'

> 1138 == 1138
true

> NaN == NaN
false

> isNaN('wft' - 1)
true

/* boolean math */

> true + false
1

> true + true == true
false

/* construct function */

> new 0xff.constructor.constructor('console.error("WTF")')()
WTF

> new Function('console.error("WTF")')()
WTF

/* typeof/instanceof */

> Array instanceof Array
false

> new Array instanceof Array
true

> Math instanceof Math
TypeError: Expecting a function in instanceof check, but got #<Object>
    at repl:1:18
    at REPLServer.self.eval (repl.js:110:21)
    at Interface.<anonymous> (repl.js:239:12)
    at Interface.emit (events.js:95:17)
    at Interface._onLine (readline.js:203:10)
    at Interface._line (readline.js:532:8)
    at Interface._ttyWrite (readline.js:761:14)
    at ReadStream.onkeypress (readline.js:100:10)
    at ReadStream.emit (events.js:98:17)
    at emitKey (readline.js:1096:12)
>