javascript adding properties to function, string and array

prop.js

function echo(input) { console.log(input);}
undefined
echo('hallo')
VM304:2 hallo
undefined
// you can add an attribute to a function
echo.prop = 'echooo'
"echooo"
echo.prop
"echooo"

// you can't add an attribute to a literal string
var a = 'asdf'
undefined
a.prop = 'qwer'
"qwer"
a.prop
undefined

// but you can add an attribute to a new String() object 
var a = new String('asdf')
undefined
a.prop = 'qwer'
"qwer"
a.prop
"qwer"

// and you can as well add an attribute to an array
var a = [1,2,3]
undefined
a.prop = 'qwer'
"qwer"
a.prop
"qwer"