js-boolean-eval-and-more.js

/**
 *  ♫ A Little Reminder About JavaScript Boolean Evaluations  ♫
 */

!!0           // false
!!NaN         // false

!![]          // true
!!new Array   // true

!!{}          // true
!!new Object  // true

!!''          // false
!!new String  // true, mmh mmh... †

!!null        // false
!!undefined   // false

!!new Date    // true


// †
/**
 *  ♫ A Little Study About How JavaScript Strings Are (a little bit) Fucked  ♫
 */

'' === new String  // false
'' == new String   // true

// Because...
''                 // ""
new String         // "[object Object]"
typeof ''          // "string"
typeof new String  // "object"

// ...and...
(new String).toString()  // ""
''.toString()            // ""

// So a string can be either an Object or a String,
//   but I have yet to find what difference it makes,
//   since in both cases it has all the string methods and properties...
(new String).length          // 0
('').length                  // 0
(new String).indexOf('foo')  // -1
('').indexOf('foo')          // -1

(new String).__proto__      // the whole thing
('').__proto__              // that same whole thing