This question is really broad, so I'm going to focus in on this part at a high level:
I tried very hard to look for relevant articles but all I can find are basic "one-time" api calls, what am I supposed to do for an entire batch of operations?
I'm guessing when you talk about requests and APIs you're talking about HTTP requests and REST APIs, which are fundamentally "stateless" kinds of things; HTTP requests are self-contained, and the backend doesn't have to keep track of any application state between requests in order to speak HTTP.
But backend applications usually do maintain state, often in the form of databases. For example, many REST APIs expose CRUD (create, read, update, and delete) operations for important business entities — in fact, Stack Overflow probably does exactly this for answers. When I post this answer, my browser will probably send some kind of a "create" request, and when I inevitably notice and fix a typo I will send some kind of "update" request. When you load it in your browser, you will send a "read" request which will get the text of the answer from Stack Overflow's database. Stack Overflow's backend keeps track of my answer between the requests, which makes it possible to send it to many users as part of many different requests.
Your frontend will have to do something similar if your project does things which involve multiple interdependent requests — for example, you would need to keep track of whether the user is authenticated or not in order to show them the login screen, and you would need to hold onto their authentication token to send along with subsequent requests.
Edit: Let's walk through a specific example. As a user, I want to be able to create and read notes. Each note should have a unique ID and a string for its text. On the backend, we'll have a set of CRUD endpoints:
var express = require(“express”);
var router = express.Router();
class Note {
constructor(id, text) {
this.id = id;
this.text = text;
}
}
// This is a quick and dirty database!
notes = {};
router.put("/note/:id", function(req, res) {
notes[req.params.id] = "hello"; // TODO: accept text as well
res.send("");
});
router.get(“/note/:id”, function(req, res) {
res.send(notes[req.params.id].text);
});
module.exports = router;
Then on the client side, one could create a note and then read it like this:
// this request will create the note
fetch("http://localhost:9000/note/42", { method: 'PUT', body: 'hello note!' });
// this request will read the note, but only after it is created!
fetch("http://localhost:9000/note/42")
.then(res => res.text())
.then(res => console.log(res));
