JSFiddle - React, Tailwind, and code Playground

JavaScript

var origin = ['a', 'b', 'c', 'd', 'e', 'f', 'g'];
var choosenKeys = [3, 2, 0];
alert(getChoosenItems(origin, choosenKeys));

function getChoosenItems(origin, choosenKeys) {
    var result = [];
    for (var i = 0; i < choosenKeys.length; i++) {
        result.push(origin[choosenKeys[i]]);
    }
    return result.sort();
}