Basically you can sort arrays with method sort, but if you want to sort objects then you have to pass function to sort method of array, so I will give you an example using your array
user = [
{
bio: "<null>",
email: "user@domain.example",
firstname: "Anna",
id: 318,
last_avatar: "<null>",
last_message: "<null>",
lastname: "Nickson",
nickname: "anny",
},
{
bio: "<null>",
email: "user@domain.example",
firstname: "Senad",
id: 318,
last_avatar: "<null>",
last_message: "<null>",
lastname: "Nickson",
nickname: "anny",
},
{
bio: "<null>",
email: "user@domain.example",
firstname: "Muhamed",
id: 318,
last_avatar: "<null>",
last_message: "<null>",
lastname: "Nickson",
nickname: "anny",
},
];
var ar = user.sort(function (a, b) {
var nA = a.firstname.toLowerCase();
var nB = b.firstname.toLowerCase();
if (nA < nB) return -1;
else if (nA > nB) return 1;
return 0;
});