Promises example in JS and JSOM

 function getListItemByID(listName, itemID) {
return new Promise(function(resolve, reject) {
//debugger;
context = SP.ClientContext.get_current();
        web = context.get_web();
        oList = web.get_lists().getByTitle(listName);

        var currentItem = oList.getItemById(itemID);

        context.load(currentItem);
        context.executeQueryAsync(
            function () {
                resolve(currentItem);
            },
            function (sender, args) {
                reject(args.get_message());
            }
        );
});
};


getListItemByID("Milestones",843)
.then(row=>getListItemByID("Process List",row.get_item("Process_x0020_ID")))
.then(row=>console.log(row.get_item("Process_x0020_Name")))
.catch(error=>console.error(error))