how well do you know your “null”s and “undefined”s?

write down what you expect the result of each operation to be. run them in a javascript console (Chrome, Firefox/Firebug, Safari). compare, verify, contrast, and, for fun, give yourself a score out of “3/4 donut”.

// Equality
null == undefined
null === undefined
!null == !undefined
!null === !undefined

// addition and concatenation
null + ''
undefined + ''
null + 1
undefined + 1

// fun with enumerations
test = []; test.push(null); console.log(test)
test = []; test.push(undefined); console.log(test)
{null:2}
{undefined:2}
{a:null}
{a:undefined}

[More programming riddles]