var obj_arr = [
{first_s: 'bbb', last_s: 'yyy'},
{first_s: 'ccc', last_s: 'zzz'},
{first_s: 'eee', last_s: 'www'},
{first_s: 'aaa', last_s: 'xxx'}
];
obj_arr = obj_arr.sort((a, b) => a.first_s > b.first_s);
console.log(obj_arr);
/*
run:
[{
first_s: "aaa",
last_s: "xxx"
}, {
first_s: "bbb",
last_s: "yyy"
}, {
first_s: "ccc",
last_s: "zzz"
}, {
first_s: "eee",
last_s: "www"
}]
*/