1.js

/x/==x

2.js

var x = function (){ 
            return function(){ 
                return function() { 
                    return false; 
                }; 
            }; 
        };

x() === x()() === x()()()

3.js

var x = {
    valueOf : function(){
        this.valueOf = function(){ return 1; }
        return 3;
    }
};

x > 2 && x < 2

4.js

function f(){}
f.prototype = {a: true};
var x = new f();

delete x.a && x.a;

5.js

var x = {};
x[x] = x;

x[x]==x

6.js

var x = function(){ x = ''; }

typeof new x < typeof x

7.js

var x = Infinity;

x - 1 === x + 1

wow, VERY nice solution to 2.js. :)

@getify Ha thanks! Unfortunately 1.js had me stumped.

@cjwainwright 1.js is stupidly easy. odds are you're over-thinking it. it's got a red herring in it. ;-)

@getify Yeah, have since seen other's solutions. Don't know what I was thinking, hopefully I would've got it if it was ({}==x) or []==x. Anyway, it's made me re-check the spec for equality comparison, which is always a good thing :-)