Creating documents in Express

Introduction

Creating documents means making new files or data entries on the server. This helps store information like user details or messages.

When a user signs up and you want to save their info.

When someone submits a form and you need to keep their answers.

When you want to add a new blog post or article to your website.

When you want to save a new product in an online store.

When you want to log events or actions happening in your app.

Syntax

Express

app.post('/path', (req, res) => {
  // get data from req.body
  // save data to database or file
  res.send('Document created')
})

Use app.post to handle creating new data because POST means sending new info.

Access the data sent by the user with req.body after using middleware like express.json().

Examples

This example creates a new user from the data sent in the request.

Express

app.post('/users', (req, res) => {
  const user = req.body
  // pretend to save user
  res.send(`User ${user.name} created`)
})

Here, a new note is created and the server responds with status 201 meaning 'created'.

Express

app.post('/notes', (req, res) => {
  const note = req.body
  // save note to database
  res.status(201).send('Note created')
})

Sample Program

This program creates a simple Express server that accepts POST requests to /documents. It expects a JSON body with title and content. If both exist, it saves the document in an array and replies with a success message.

Express

import express from 'express'

const app = express()
app.use(express.json())

const documents = []

app.post('/documents', (req, res) => {
  const doc = req.body
  if (!doc.title || !doc.content) {
    return res.status(400).send('Missing title or content')
  }
  documents.push(doc)
  res.status(201).send(`Document titled '${doc.title}' created`)
})

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

Important Notes

Always use express.json() middleware to read JSON data sent by clients.

Use status code 201 to clearly say a new resource was created.

Validate the incoming data to avoid saving incomplete documents.

Summary

Use app.post to create new documents or data entries.

Access user data with req.body after enabling JSON parsing.

Send a clear response with status 201 when creation is successful.

Practice

1. Which Express method is used to handle creating new documents via HTTP POST requests?

easy

A. app.post()

B. app.get()

C. app.put()

D. app.delete()

Solution

1. Step 1: Understand HTTP methods in Express

   Express uses different methods like get, post, put, and delete to handle HTTP requests.

2. Step 2: Identify method for creating new data

   The post method is used to create new documents or data entries.

3. Final Answer:

   app.post() -> Option A

4. Quick Check:

   Creating documents = app.post() [OK]

Hint: Use app.post() for creating new data entries [OK]

Common Mistakes:

• Using app.get() instead of app.post()
• Confusing app.put() with app.post()
• Using app.delete() for creation

2. Which code snippet correctly enables JSON parsing middleware in Express to access req.body?

easy

A. app.use(express.urlencoded());

B. app.use(express.json());

C. app.use(bodyParser.text());

D. app.use(express.static('public'));

Solution

1. Step 1: Identify middleware for JSON parsing

   Express provides express.json() middleware to parse JSON request bodies.

2. Step 2: Match correct usage

   The correct way is app.use(express.json()); to enable JSON parsing.

3. Final Answer:

   app.use(express.json()); -> Option B

4. Quick Check:

   JSON parsing middleware = express.json() [OK]

Hint: Use app.use(express.json()) to read JSON body [OK]

Common Mistakes:

• Using express.urlencoded() for JSON data
• Using bodyParser.text() instead of JSON parser
• Forgetting to enable any parser middleware

3. What will be the HTTP status code sent when the following Express route successfully creates a document?

app.post('/items', (req, res) => {
  // Assume document creation here
  res.status(201).send('Created');
});

medium

A. 200

B. 500

C. 400

D. 201

Solution

1. Step 1: Understand HTTP status codes for creation

   Status code 201 means "Created" and is used when a new resource is successfully created.

2. Step 2: Check the code's status method

   The code uses res.status(201), so it sends status 201.

3. Final Answer:

   201 -> Option D

4. Quick Check:

   Creation success status = 201 [OK]

Hint: Use status 201 for successful creation responses [OK]

Common Mistakes:

• Assuming 200 means creation success
• Using 400 or 500 for successful creation
• Not setting status code explicitly

4. Identify the error in this Express route for creating a document:

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

medium

A. saveUser function is not asynchronous

B. Using res.send instead of res.json

C. Missing JSON parsing middleware to read req.body

D. Route should use app.get instead of app.post

Solution

1. Step 1: Check access to req.body

   Without JSON parsing middleware, req.body will be undefined.

2. Step 2: Identify missing middleware

   The code does not show app.use(express.json()), so req.body won't work.

3. Final Answer:

   Missing JSON parsing middleware to read req.body -> Option C

4. Quick Check:

   Missing express.json() causes req.body undefined [OK]

Hint: Always enable express.json() before accessing req.body [OK]

Common Mistakes:

• Thinking res.send must be res.json
• Using app.get for creation routes
• Assuming saveUser must be async here

5. You want to create an Express route that accepts JSON data to create a new product and respond with the created product including an ID. Which code snippet correctly implements this?

hard

A. app.post('/products', (req, res) => {
const product = req.body;
product.id = Date.now();
res.status(201).json(product);
});

B. app.get('/products', (req, res) => {
const product = req.body;
product.id = Date.now();
res.json(product);
});

C. app.post('/products', (req, res) => {
const product = req.query;
product.id = Date.now();
res.status(200).send(product);
});

D. app.post('/products', (req, res) => {
const product = req.body;
res.send('Product created');
});

Solution

1. Step 1: Use correct HTTP method and access JSON body

   The route uses app.post and accesses req.body which is correct for creating a product.

2. Step 2: Add an ID and respond with status 201 and JSON

   Assigning product.id = Date.now() simulates creating an ID. Responding with res.status(201).json(product) sends the created product with proper status.

3. Final Answer:

   Option A code snippet -> Option A

4. Quick Check:

   POST + req.body + status 201 + json response = app.post('/products', (req, res) => { const product = req.body; product.id = Date.now(); res.status(201).json(product); }); [OK]

Hint: Use app.post with req.body and res.status(201).json() [OK]

Common Mistakes:

• Using app.get instead of app.post
• Reading data from req.query instead of req.body
• Not sending status 201 on creation