How to Create REST API with Express: Simple Guide

To create a REST API with Express, first install Express and set up a server using express(). Then define routes with HTTP methods like GET, POST, PUT, and DELETE to handle API requests and send responses.

Syntax

Here is the basic syntax to create a REST API endpoint in Express:

• const express = require('express'): Import Express library.
• const app = express(): Create an Express app instance.
• app.use(express.json()): Middleware to parse JSON request bodies.
• app.METHOD(PATH, HANDLER): Define a route where METHOD is HTTP method like GET, POST, etc., PATH is the URL path, and HANDLER is a function to process requests.
• app.listen(PORT): Start the server on a port.

javascript

const express = require('express')
const app = express()

app.use(express.json())

app.get('/path', (req, res) => {
  res.send('response')
})

app.listen(3000, () => {
  console.log('Server running on port 3000')
})

Example

This example creates a simple REST API with Express that manages a list of items. It supports getting all items, adding a new item, updating an item by id, and deleting an item by id.

javascript

import express from 'express'
const app = express()
app.use(express.json())

let items = [{ id: 1, name: 'Item One' }]

// Get all items
app.get('/items', (req, res) => {
  res.json(items)
})

// Add a new item
app.post('/items', (req, res) => {
  const newItem = { id: Date.now(), name: req.body.name }
  items.push(newItem)
  res.status(201).json(newItem)
})

// Update an item by id
app.put('/items/:id', (req, res) => {
  const id = Number(req.params.id)
  const item = items.find(i => i.id === id)
  if (!item) return res.status(404).json({ error: 'Item not found' })
  item.name = req.body.name
  res.json(item)
})

// Delete an item by id
app.delete('/items/:id', (req, res) => {
  const id = Number(req.params.id)
  items = items.filter(i => i.id !== id)
  res.status(204).end()
})

app.listen(3000, () => {
  console.log('API running on http://localhost:3000')
})

Output

API running on http://localhost:3000

Common Pitfalls

Common mistakes when creating REST APIs with Express include:

• Not using express.json() middleware, so JSON request bodies are undefined.
• Forgetting to send a response, causing requests to hang.
• Not handling errors or missing resources, leading to unclear client responses.
• Using app.get for all routes instead of proper HTTP methods.

javascript

/* Wrong: Missing express.json middleware */
const express = require('express')
const app = express()

app.post('/data', (req, res) => {
  // req.body will be undefined
  res.send(req.body)
})

app.listen(3000)

/* Right: Add express.json middleware */
app.use(express.json())

Quick Reference

Here is a quick reference for common Express REST API methods:

HTTP Method	Express Method	Purpose
GET	app.get(path, handler)	Retrieve data from server
POST	app.post(path, handler)	Create new data on server
PUT	app.put(path, handler)	Update existing data
DELETE	app.delete(path, handler)	Remove data from server

Key Takeaways

Use express.json() middleware to parse JSON request bodies.

Define routes with app.get, app.post, app.put, and app.delete for RESTful API.

Always send a response to avoid hanging requests.

Handle errors and missing data with proper status codes.

Start the server with app.listen on a chosen port.