Algorithm to get changes between two arrays

Question

I needed to create an algorithm which will (efficiently) take an old array and a new array and give me back the changes between the two (which items added, which removed). It ha

Answer 1

// I prefer to not sort the arrays

Array.prototype.diff= function(ar){
    var a= [], i= 0, L= this.length,
    ar= ar.concat(), t1, t2;
    while(i