1.js

var x = '/x/';
/x/==x

2.js

function x() { if (x._val > 5) return true; x._val = (x._val || 1) + 1; return x; }
x() === x()() === x()()()

3.js

var x = { _val: -3, valueOf: function() { return (this._val *= -1); }};
x > 2 && x < 2

4.js

var x = (function(){ 
  function F(){}
  F.prototype.a = true;
  return new F();
})();
delete x.a && x.a;

5.js

var x = {};
x["[object Object]"] = x;
x[x]==x

6.js

function x() { x = {}; return function(){}; }
typeof new x < typeof x

7.js

var x = Infinity;
x - 1 === x + 1