var d = $.Deferred();
var promise = d.resolve('abc');

promise.done(function (x) { // Suppose promise returns "abc"
    console.log(x);
    return 123;
}).done(function (x){
    console.log(x);
  // return is omitted
}).done(function (x){
    console.log(x)
})

/*
abc
123
undefined
*/