JS string weirdness

strings.js

/*Strings aren't objects.*/
typeof ''               // 'string'
'' instanceof Object    // false

/*But they have methods.*/
'a'.concat(' string');  // 'a string'

/*A string's methods are equal across receivers.*/
'a'.concat === 'b'.concat // true

/*String's methods (capital S) aren't.*/
(new String('a')).concat === (new String('b')).concat   // false
/*Even though a method isn't bound to its receiver.*/
var m = (new String('a')).concat
m(' string')    // TypeError: can't convert undefined to object (receiver is undefined)

/*And a String's methods (capital S) return strings (lowercase S).*/
typeof new String('a')                      // 'Object'
typeof (new String('a')).concat(' string')  // 'string'

/*loljs*/

Ah wait a minute. This turns out to be true:

a = (new String('a')).concat
b = (new String('b')).concat
a === b // true

Which vaguely makes sense. Once concat is assigned to a and b, neither has a receiver, so they're finally equal.