PUT and PATCH route handling in Express - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

Difference in behavior between PUT and PATCH routes

Consider an Express app with two routes: one handling PUT /user/:id and another handling PATCH /user/:id. Both update user data in a database.

What is the main difference in how these routes should behave when updating a user?

A Both PUT and PATCH always update only the specified fields.

B PATCH replaces the entire user object, while PUT updates only the specified fields.

C PUT replaces the entire user object, while PATCH updates only the specified fields.

D Both PUT and PATCH always replace the entire user object.

💡 Hint

Think about full replacement versus partial update.

PUT is meant to replace the entire resource, so the server expects a full user object. PATCH is for partial updates, so only the fields to change are sent.

📝 Syntax

intermediate

Correct syntax for defining a PATCH route in Express

Which of the following code snippets correctly defines a PATCH route for updating a user's email in Express?

Express

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

A app.PATCH('/user/:id', (req, res) => { /* update email */ });

B app.patch('/user/:id', (req, res) => { /* update email */ });

C app.patch('/user/:id', function updateEmail(req, res) { /* update email */ });

D app.patch('/user/:id', async (req, res) => { /* update email */ });

💡 Hint

Check method name casing and syntax.

Express methods are lowercase. Both arrow functions and named functions work, but the question asks for correct syntax, so uppercase method is invalid.

🔧 Debug

advanced

Why does this PUT route not update the user correctly?

Given this Express PUT route code, why does the user data not update as expected?

Express

app.put('/user/:id', (req, res) => {
  const id = req.params.id;
  const newData = req.body;
  const user = users.find(u => u.id === id);
  Object.assign(user, newData);
  res.send(user);
});

A The <code>id</code> from <code>req.params</code> is a string, but user IDs are numbers, so <code>find</code> returns undefined.

B The route should use <code>PATCH</code> instead of <code>PUT</code> to update user data.

C The <code>Object.assign</code> method does not update objects in JavaScript.

D The <code>res.send</code> method is missing a status code.

💡 Hint

Check data types when searching in arrays.

The id from URL params is a string, but user IDs in the array are numbers, so find returns undefined and Object.assign fails silently.

❓ state_output

advanced

Resulting user object after PATCH request

Assume the user object before the PATCH request is:

{"id":1,"name":"Alice","email":"[e-mail]","age":30}

The PATCH request body is:

{"email":"[e-mail]","age":31}

What will the user object look like after the PATCH route updates it with Object.assign(user, req.body)?

A {"id":1,"name":"Alice","email":"[e-mail]","age":30}

B {"email":"[e-mail]","age":31}

C {"id":1,"name":"Alice"}

D {"id":1,"name":"Alice","email":"[e-mail]","age":31}

💡 Hint

Think about how Object.assign merges objects.

Object.assign updates existing properties and adds new ones but keeps properties not overwritten. So only email and age change.

🧠 Conceptual

expert

Why prefer PATCH over PUT for partial updates in REST APIs?

In REST API design, why is it generally better to use PATCH instead of PUT when updating only some fields of a resource?

A PATCH allows partial updates without sending the entire resource, reducing bandwidth and risk of overwriting data.

B PUT and PATCH have identical behavior, so it does not matter which one is used.

C PATCH requires the client to send the full resource, which ensures data consistency.

D PUT is faster than PATCH because it replaces the whole resource at once.

💡 Hint

Consider network efficiency and data safety.

PATCH updates only specified fields, so clients send less data and avoid accidentally overwriting fields they don't intend to change. PUT replaces the entire resource, which can cause data loss if fields are missing.