In full-stack development, we often write code for both the frontend and the backend. The frontend manages the user interface, while the backend manages the database, logic, and APIs. Usually, these two sides are built using different tools or frameworks, but they often need to do similar things — like validate user input, format dates, or handle error messages.
Instead of writing the same code twice, developers can create shared libraries. These libraries allow code to be reused across both the frontend and backend. This saves time, reduces bugs, and keeps your codebase clean and consistent.
When learning full-stack development through full stack java developer training, shared libraries are an important topic because they help students write smarter and more efficient code.
What Is a Shared Library?
A shared library is a folder or package that contains code which can be used in both the frontend and backend of a full-stack app. This code might include:
- Validation logic (like checking if an email is valid)
- Formatting functions (like showing dates in the same format)
- Constants (like user roles or status messages)
- Reusable components or functions
Instead of writing this logic twice, once in the backend (like in Node.js) and once in the frontend (like in React), you can write it once and share it across both.
Why Is Code Reusability Important?
Writing reusable code helps in many ways:
- Saves Time
- You only write and test code once, not twice.
- Reduces Bugs
- If a validation rule changes, you only need to update it in one place.
- Keeps Code Clean
- Shared logic keeps your app organized.
- Better Collaboration
- Teams can work faster because they trust the shared code works the same everywhere.
These are some of the reasons why shared libraries are taught in many full stack developer course in Hyderabad, where the focus is on building scalable and real-world applications.
Real-Life Example
Let’s say you’re building a signup form in your full-stack app. You want to:
goog_949281284- Inspect if the email is in the correct format
- Make sure the password is at least 8 characters
- Ensure both passwords match
- You can write a validation function like this:
function validateSignup(data) {
const errors = {};
if (!data.email.includes("@")) {
errors.email = "Email is not valid";
}
if (data.password.length < 8) {
errors.password = "Password must be at least 8 characters";
}
if (data.password !== data.confirmPassword) {
errors.confirmPassword = "Passwords do not match";
}
return errors;
}
Now, instead of writing this function twice — once in your frontend and once in your backend — you put it in a shared library and use it in both places.
How to Create a Shared Library
Let’s go through the simple steps to create a shared library in a Node.js + React project.
Step 1: Set Up Project Structure
Create a new folder called shared inside your project root.
my-app/
│
├── backend/
├── frontend/
├── shared/
│ └── validators.js
Step 2: Write Reusable Code
Inside validators.js, add your shared functions:
// shared/validators.js
function isEmailValid(email) {
return email.includes("@");
}
function isPasswordStrong(password) {
return password.length >= 8;
}
module.exports = {
isEmailValid,
isPasswordStrong,
};
Step 3: Use in Backend
In your backend (Node.js), you can import the shared functions:
const { isEmailValid, isPasswordStrong } = require("../shared/validators");
app.post("/signup", (req, res) => {
const { email, password } = req.body;
if (!isEmailValid(email)) {
return res.status(400).send("Invalid email");
}
if (!isPasswordStrong(password)) {
return res.status(400).send("Weak password");
}
// Proceed with signup...
});
Step 4: Use in Frontend
In React, use the same code with a bundler like Webpack or a shared NPM package:
import { isEmailValid, isPasswordStrong } from "../../shared/validators";
function handleSignup() {
if (!isEmailValid(email)) {
alert("Invalid email");
}
if (!isPasswordStrong(password)) {
alert("Weak password");
}
// Continue form submission...
}
Using Shared Code with TypeScript
If you’re using TypeScript, shared libraries become even more powerful. You can add type definitions to ensure your data is correct across your app.
export interface UserData {
email: string;
password: string;
}
export function validateEmail(email: string): boolean {
return email.includes("@");
}
Both the frontend and backend will now get proper type checking and autocomplete. This helps avoid errors and improves developer experience.
What to Include in a Shared Library
Here are some ideas of what you can include:
goog_949281286- Validation functions
- Formatting helpers (currency, date, numbers)
- Constants (like API URLs, error codes)
- Enums (user roles, order status)
- Business logic (like calculating discounts)
- You can even split your shared folder into multiple files if needed:
shared/
│
├── validators.js
├── formatters.js
├── constants.js
When Not to Share Code
While shared libraries are helpful, not everything should be shared. Avoid putting:
goog_949281288- Frontend-only logic (like animations or UI themes)
- Backend-only logic (like database queries or environment variables)
Only share code that makes sense on both sides.
Using NPM Packages for Sharing
In larger projects, developers turn their shared libraries into NPM packages. You can publish your shared code as a private package and install it in both frontend and backend.
This is helpful for teams working on multiple projects and wanting to share the same logic across all of them.
Benefits for Teams
For teams, shared libraries improve:
- Team speed (less repeated work)
- Code quality (shared testing)
- Team collaboration (everyone uses the same rules)
That’s why many students attending full stack developer classes are encouraged to build projects that include shared libraries between frontend and backend.
Hosting Shared Code in Monorepos
Many teams use a structure called a monorepo, where all frontend, backend, and shared code live in the same Git repository.
This makes it easier to:
- Keep shared code in sync
- Avoid version conflicts
- Simplify development
Tools like Nx, Lerna, and Turborepo are popular for managing monorepos with shared libraries.
Challenges and Solutions
Like any system, shared libraries come with challenges:
1. Keeping Everything Updated
Solution: Use version control carefully and update dependencies together.
2. File Path Issues
Solution: Use relative paths or configure alias imports for shared folders.
3. Testing Shared Code
Solution: Write tests inside the shared folder so you can run them easily in both frontend and backend.
Final Thoughts
Shared libraries help full-stack developers write clean, reusable, and consistent code. By using shared logic for validation, formatting, and constants, teams can save time and avoid repeating themselves.
This is especially helpful when building projects quickly or working with a team. If you're just starting out in a full stack developer course in Hyderabad, practicing code reusability will help you become a better developer and write smarter apps.
As apps grow, maintaining code becomes harder. Shared libraries make it easier. They reduce bugs, make updates simpler, and help you deliver high-quality apps faster.
So whether you're working on a personal project or building software in a team, consider using shared libraries to power your full-stack development. It’s a small step that brings big results.
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