In Express.js, a popular Node.js web framework, req is an object that represents the HTTP request. It has several properties that allow you to access data sent with the request. Here's a breakdown of the differences between req.body, req.query, and req.params:

req.body

• Contains the parsed body of the request, typically used for POST, PUT, and PATCH requests.
• The body can be in various formats, such as JSON, URL-encoded, or multipart/form-data.
• To access req.body, you need to use a middleware like body-parser or express.json().

req.query

• Contains the query string parameters of the request, typically used for GET requests.
• The query string is the part of the URL that comes after the ? symbol.
• req.query is an object where the keys are the parameter names and the values are the parameter values.

req.params

• Contains the route parameters of the request, typically used for routes with parameterized paths.
• Route parameters are defined in the route path using a colon (:) followed by the parameter name.
• req.params is an object where the keys are the parameter names and the values are the parameter values.

Here's an example to illustrate the differences:

const express = require('express');
const app = express();
app.use(express.json());

// Route with route parameter
app.get('/users/:id', (req, res) => {
  console.log(req.params); // { id: '123' }
  res.send(`User ID: ${req.params.id}`);
});

// Route with query string parameters
app.get('/products', (req, res) => {
  console.log(req.query); // { category: 'electronics', price: '100' }
  res.send(`Products: ${req.query.category} ${req.query.price}`);
});

// Route with request body
app.post('/orders', (req, res) => {
  console.log(req.body); // { productId: '123', quantity: 2 }
  res.send(`Order placed: ${req.body.productId} x ${req.body.quantity}`);
});

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