the-truthiness-of-strings.js

// Empty strings are truthy-falsy...

var EMPTY = "";
    EMPTY == true;          // false
    EMPTY == false;         // true

// ...but non-empty strings are NOT.        
                                            
var NON_EMPTY = "hello, world";
    NON_EMPTY == true;      // false
    NON_EMPTY == false;     // false

// Neither are "true" nor "false"...        
                                            
var FALSE = "false";                        
    FALSE == true;          // false
    FALSE == false;         // false

var TRUE = "true";                          
    TRUE == true;           // false
    TRUE == false;          // false

// ...nor "undefined" nor "null".           
                                            
var UNDEFINED = "undefined";                
    UNDEFINED == true;      // false
    UNDEFINED == false;     // false

var NULL = "null";                          
    NULL == true;           // false
    NULL == false;          // false

// But numeric strings are truthy-falsy...

var ZERO = "0";
    ZERO == true;           // false
    ZERO == false;          // true

var ONE = "1";                              
    ONE == true;            // true
    ONE == false;           // false

// ...as long as they are only "0" or "1".

var TWO = "2";                             
    TWO == true;            // false
    TWO == false;           // false

var NEGATIVE_ONE = "-1";
    NEGATIVE_ONE == true;   // false
    NEGATIVE_ONE == false;  // false