returnTrue

Help

Demo: http://codepen.io/i0z/pen/GqPKKA?editors=1010

Demo: http://codepen.io/i0z/pen/pbGqVZ?editors=1010

---

Reflexive

function reflexive(x) {
    return x != x;
}

reflexive(NaN)

Transitive

function transitive(x,y,z) {
    return x && x == y && y == z && x != z;
}

transitive([],0,[]) 

Counter

function counter(f) {
    var a = f(), b = f();
    return a() == 1 && a() == 2 && a() == 3
        && b() == 1 && b() == 2;
}

counter((x=1)=>$=>x++)
counter(x=>$=>x=-~x)   // -2 symbols

Peano

chrome 54

function peano(x) {
    return (x++ !== x) && (x++ === x);
}

peano(2**53-1)

Array

function array(x,y) {
    return Array.isArray(x) && !(x instanceof Array) &&
          !Array.isArray(y) &&  (y instanceof Array);
}

array( a=Array.prototype,{__proto__:a})
array( (Array.isArray=x=>x[0],'1'),[] )
array( '1',[],Array.isArray=x=>x[0]   )
array( Array.isArray=x=>x.length,[]   )
array( Array.isArray=$=>x--,[],x=1    )
array( 0,[Array.isArray=>x=>!x]       )
array( [].__proto__,{__proto__:[]}    )
array( x=[],x.__proto__=null,x),Object.create([]) ) // = 43
array( Array.isArray=String,[]        ) // = 23

Instance

function instance(x,y) {
  return x instanceof y && y instanceof x && x !== y;
}

instance(Object,Function)
instance(Object,Proxy)

Instance2

function instance2(a,b,c) {
  return a !== b && b !== c && a !== c
      && a instanceof b
      && b instanceof c 
      && c instanceof a;
}

Object,Function,{[Symbol.hasInstance]:_=>!0}   44
a=Object,Function,{[Symbol.hasInstance]:a}     42
a=Object,Function,c=_=>_,c.__proto__=a         38
a=Object,Function,new Proxy(a,a)               32
a=Object,a.bind(),a.bind()                     26

Proto1

function proto1(x) {
    return x && !("__proto__" in x);
}

proto1(Object.create(null))
proto1({__proto__:null})

Undef

function undef(x) {
    return !{ undefined: { undefined: 1 } }[typeof x][x];
}

undef((Object.prototype['number']=0,0))
undef(document.all)

Symmetric

function symmetric(x,y) {
    return x == y && y != x;
}

symmetric(1,{valueOf:$=>n=-~this.n})
symmetric(n=1,{valueOf:$=>n++})

Ouroborobj

function ouroborobj(x) {
    return x in x;
}

ouroborobj([0])

Truth

function truth(x) {
    return x.valueOf() && !x;
}

truth((Number.prototype.valueOf=$=>1,0))
truth('',''.__proto__.valueOf=_=>1)
truth(0,0..__proto__.valueOf=_=>1)

Wat

function wat(x) {
    return x('hello') == 'world:)' && !x;
}

wat([a]=document.all,a.id='hello',a.valueOf=_=>'world:)');

Evil1

var eval = window.eval;
function evil1(x) {
    return eval(x+'(x)') && !eval(x)(x);
}

evil1($=>0)

Evil2

var eval = window.eval;
function evil2(x) {
    return eval('('+x+')(x)') && !eval(x)(x);
}

evil2($=>x,x=0)

Random1

function random1(x) {
    return Math.random() in x;
}

random1((Math.random=$=>0,[0]))
random1(Math.random=$=>'call')
random1([0],Math.random=_=>0)
random1([Math.random=_=>0])

Random2

{
	let rand = Math.random();
	function random2(x) {
	  return rand in x;
	}
}

random2(new Proxy({},{has:$=>$}))

Random3

var key = crypto.getRandomValues(new Uint32Array(4));
function random3(x) {
    var d = 0;
    for (var i=0; i<key.length; i++) {
        d |= key[i] ^ x[i];
    }
    return d === 0;
}

random3(Object.defineProperty(Uint32Array.prototype, 'length', {value: 0}))
random3(Uint32Array.prototype.__defineGetter__('length',$=>0))

Random4

{
	let rand = Math.random();
	function random4(x) {
	    return rand === x;
	}
}

random4(impossible)

---

New my level :)

Greaterself

function greaterself(x) {
    return x > 8 && 8 > x;
}

greaterself({n:0,valueOf:function(){return++this.n%2?9:7}})
greaterself({valueOf:$=>(n=-~this.n)%2?9:7})

Closure

function closure(x) {
    return x[x] == x;
}

closure([0]);

Any

function any(x) {
    return x - 1 === x + 1
}

any(2**54)
any(1/0)

Isarray

function isarray(x) {
    return Array.isArray(x) && x instanceof Array && x.map === undefined
}

isarray(new Proxy([],{get:(o,p)=>p=='map'?void 0:o[p]}))

Brainfuck

function brainfuck(x) {
	return x(/2/ << /3/) === 16;
}

brainfuck((RegExp.prototype.valueOf=function(){return this.source},x=>x))

Native code

{
	const toString = Function.prototype.toString;
	function native(x) {
		return	(x() === 1) &&
				(x.toString() === 'function () { [native code] }') &&
				(toString.call(x) === x.toString())
	}
}

function(){return 1}.bind(null)
(_=>1).bind()

Instance2

function instance2(x,y) {
  return x instanceof y && y instanceof x && x == y;
}

instance2(Function, Function)
instance2(x=Function, x)

Minest

{
  let v = parseFloat('0.00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000001')
  
  function minest(x) {
    return x > 0 &&
           x < v &&
           x.toString().length <= 6
  }
}

minest( Number.MIN_VALUE )

Reflexive2

function reflexive2(x) {
	return 'number' == typeof x && x != x
}
reflexive2(NaN);

Numbers

function num1(a) { // new Number(1)
	return a == 1 && a instanceof Number
}

function num2(a) { // Nan
	return typeof a == 'number' && !(a instanceof Number)
}

Sum1

function summ1(x, y) {
	return x + y === 0.3
}
summ1(0, 0.3);

Summ2

function summ2(x, y) {
	return x + 0.2 === 0.3
}

summ2(0.09999999999999998);

IsObject

function isObject(x) {
	return (typeof x == 'object') && !(x instanceof Object)
}

isObject(null);

UndefinedObject

function undefinedObject(x) {
	return typeof x == 'undefined' && x instanceof Object;
}

undefinedObject(document.all);

Joke

function joke(s, x) {
	return s == new x(s.length +1);
}

joke(',,,', Array);

Eval evil

function eval_evil(x) {
	return x[x][x]("return true")();
}

eval_evil('constructor')

New

function _new(x) {
	return new x instanceof x;
}

_new( function(){} )
_new( class A{}    )

New2

function _new2(x) {
	return x() instanceof x;
}

_new2( function a(){ if(!(this instanceof a)) return new a } );

New3

function _new(x) {
	return x() instanceof x && x.name === '';
}

_new(function(){if(!(this instanceof arguments.callee))return new arguments.callee})

Foo

function foo(f) {
	var o = { x: 'x' }
	function x(x) { return this.x === o[x] }
	return f(o, x);
}

foo((o,x)=>x.bind(o,'x')())
foo((o,x)=>x.call(o,'x')())

Random2.1 (if has access to global scope)

var rand = Math.random();
function random21(x) {
  return rand in x;
}

random21({[rand]:1}))

Date

function date(x) {
    var d = new Date,
        a = [d];
    return a[x]() == d.toLocaleDateString()+', '+d.toLocaleTimeString();
}

date('toLocaleString');

Nill

function nil(x) {
  return (x != null) && (x <= null) && (x >= null)
}

nil(0)