REST APIs should accept JSON for request payload and also send responses to JSON. JSON is the standard for transferring data. Almost every networked technology can use it: JavaScript has built-in methods to encode and decode JSON either through the Fetch API or another HTTP client. Server-side technologies have libraries that can decode JSON without doing much work.
There are other ways to transfer data. XML isn’t widely supported by frameworks without transforming the data ourselves to something that can be used, and that’s usually JSON. We can’t manipulate this data as easily on the client-side, especially in browsers. It ends up being a lot of extra work just to do normal data transfer.
Form data is good for sending data, especially if we want to send files. But for text and numbers, we don’t need form data to transfer those since—with most frameworks—we can transfer JSON by just getting the data from it directly on the client side. It’s by far the most straightforward to do so.
To make sure that when our REST API app responds with JSON that clients interpret it as such, we should set Content-Type in the response header to application/json after the request is made. Many server-side app frameworks set the response header automatically. Some HTTP clients look at the Content-Type response header and parse the data according to that format.
The only exception is if we’re trying to send and receive files between client and server. Then we need to handle file responses and send form data from client to server. But that is a topic for another time.
Let’s take a look at an example API that accepts JSON payloads. This example will use the Express back end framework for Node.js. We can use the body-parser to parse the JSON request body, and then we can call the res.json method with the object that we want to return as the JSON response as follows:
const express = require('express');
const bodyParser = require('body-parser');
const app = express();
app.use(bodyParser.json());
app.post('/', (req, res) => {
res.json(req.body);
});
app.listen(3000, () => console.log('server started'));
bodyParser.json() parses the JSON request body string into a JavaScript object and then assigns it to the req.body object.
Shruti.A.M 