Javascript random array

var title = 'a', 'b';
var length = 326, '424';

how do I get a random pick from the options and make sure that if it picks 'a' then it needs to pick '326' with it and then how do you assign them a number?

For instances if it picks a it automatically needs to get 326 with it and then I need to give something like

 var title1 = (picked number) 
    var length = (picked with number)

and then the other it didn't pick I need it to make it

var title2 = (title it didn't pick)
var title2 = (didnt get picked length)