How javascript equals works

how_equals_works.js

var console = console || require('console');
function foo(n){
  this.name = n;
}
foo.prototype.toString = function(){ return this.name };

console.log(new foo('key') === 'key'); // false
console.log(null === undefined); // false
console.log(new foo('key') == 'key'); // true
console.log(null == undefined); // true
console.log(new foo('10') == 10); // true
console.log(new foo('10') < 11); // true
console.log(new foo('10') > 9); // true
console.log(new foo('1') == true); // true
console.log(new foo('0') == false); // true
console.log(!!(new foo('0'))); // true

map = {};
map['key'] = 'value';
console.log(map[new foo('key')] === 'value'); // true