1.js

/x/==x

var x = '/x/';

2.js

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

for first comparison should be returned the same value
for second - true

function x () {
  x.times = ++x.times || 1;
  return x.times > 5 ? true : x;
}
x() === x()() === x()()()

3.js

x > 2 && x < 2

valueOf property should be overwritten to cast object to primitive 

var x = {
  reverse: -1,
  val: -10,
  valueOf: function () {
    this.val = this.reverse * this.val;
    return this.val;
  }
}

4.js

delete x.a && x.a;

5.js

x[x]==x

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

6.js

typeof new x < typeof x

typeof return as result string, charCodeAt using for string comparison

function x () {
  x = 1;
  return function () {};
}

7.js

x - 1 === x + 1

var x = {
  val: -1,
  valueOf: function () {
    return (this.val = ~this.val + 1);
  }
};

/*
var x = {
  times: 0,
  valueOf: function () {
    ++this.times;
    return this.times%2 ? 1 : -1;
  }
};
*/