Why Do We Need APIs?

Imagine you open a food delivery app.

When you search for restaurants:

• the app requests data from a server

• the server sends restaurant data back

When you place an order:

• the app sends order details

• the server saves it

This communication between:

• frontend (client)

• backend (server)

happens using APIs.

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What is a REST API?

REST API is a way for:

• clients

• servers

to communicate using HTTP.

Simple meaning:

A REST API lets applications send and receive data in a structured way.

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Think of It Like a Waiter

Real-Life Analogy

• You → Client

• Kitchen → Server

• Waiter → API

Flow:

Client → API → Server
Server → API → Client

The API carries requests and responses between both sides.

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REST Request-Response Flow

Example:

1. Client sends request

2. Server processes it

3. Server sends response

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What Does REST Mean?

REST stands for:

Representational State Transfer

Sounds complicated, but don’t worry.

For beginners, REST mainly means:

• clean URLs

• proper HTTP methods

• organized API structure

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What Are Resources in REST?

In REST APIs, everything is treated as a resource.

Examples:

• users

• products

• orders

• posts

If your app manages users:

/users

Here:

• users is the resource

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Understanding Resources

Think of resources as collections of data.

Example:

/users
/products
/orders

Each resource gets its own routes.

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HTTP Methods in REST APIs

HTTP methods describe:

what action we want to perform.

Main methods:

• GET

• POST

• PUT

• DELETE

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CRUD Operations

CRUD means:

• Create

• Read

• Update

• Delete

REST APIs map CRUD operations to HTTP methods.

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CRUD vs HTTP Methods

Operation	HTTP Method
Read	GET
Create	POST
Update	PUT
Delete	DELETE

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GET Method

Used to fetch data.

Example:

GET /users

Meaning:

Give me all users.

Express example:

app.get('/users', (req, res) => {
  res.send('All users');
});

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GET Single User

GET /users/5

Meaning:

Give me user with ID 5.

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POST Method

Used to create data.

Example:

POST /users

Meaning:

Create a new user.

Express example:

app.post('/users', (req, res) => {
  res.send('User created');
});

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PUT Method

Used to update existing data.

Example:

PUT /users/5

Meaning:

Update user with ID 5.

Express example:

app.put('/users/:id', (req, res) => {
  res.send('User updated');
});

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DELETE Method

Used to remove data.

Example:

DELETE /users/5

Meaning:

Delete user with ID 5.

Express example:

app.delete('/users/:id', (req, res) => {
  res.send('User deleted');
});

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REST Route Design

Good REST APIs use clean route names.

Good Routes

/users
/users/10
/products
/orders

Simple and readable.

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Bad Routes

/getUsers
/createUser
/deleteUser

Why bad? Because HTTP methods already describe actions.

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REST Style Thinking

Instead of:

GET /getUsers

REST prefers:

GET /users

Cleaner and easier to understand.

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Status Codes Basics

When server responds, it also sends a status code.

Status codes tell:

whether request succeeded or failed.

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Common Status Codes

Code	Meaning
200	Success
201	Created
404	Not Found
500	Server Error

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Example Response

res.status(200).send('Users fetched');

Creating user:

res.status(201).send('User created');

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Full REST Example with Users

const express = require('express');

const app = express();

app.get('/users', (req, res) => {
  res.send('Get all users');
});

app.get('/users/:id', (req, res) => {
  res.send(`Get user ${req.params.id}`);
});

app.post('/users', (req, res) => {
  res.send('Create user');
});

app.put('/users/:id', (req, res) => {
  res.send(`Update user ${req.params.id}`);
});

app.delete('/users/:id', (req, res) => {
  res.send(`Delete user ${req.params.id}`);
});

app.listen(3000);

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Understanding the Flow

Example:

GET /users/10

Flow:

1. Client sends request

2. Server receives route

3. Server processes data

4. Response sent back

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Before vs After REST Design

Non-REST Style

/getAllUsers
/addNewUser
/removeUser

---

REST Style

GET /users
POST /users
DELETE /users/5

Much cleaner.

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Why REST APIs Are Popular

REST APIs are:

• simple

• readable

• organized

• scalable

Almost every modern backend application uses REST concepts.

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Practice Assignment

1. Create GET Route

Create:

GET /users

Return:

All users

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2. Create POST Route

Create:

POST /users

Return:

User created

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3. Create PUT Route

Create:

PUT /users/:id

Print user ID.

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4. Create DELETE Route

Create:

DELETE /users/:id

Return delete message.

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5. Use Status Codes

Try:

• 200

• 201

• 404

and observe responses.