In every iteration your code is setting pass to be an array that contains a single item which is the current item, so each iteration replaces the array before end meaning you end up with only the last one in the loop. Instead in your loop you need to add a single item to the existing array.
pass.push ({"title": data[i].TaskName, "start": 'Sat Dec 10 2016 16:35:55 GMT+0530 (India Standard Time)',"className": 'bg-purple'});
Above I am using push to add to the array and I am pushing a single item
{ ... }
unlike your original code which was setting an array with a single item
[{ ... }]
(an item is defined by {} and an array by [])