How to Write Secure JavaScript Code: A Developer's Guide

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How to Write Secure JavaScript Code: A Developer's Guide

How to Write Secure JavaScript Code: A Developer's Guide

November 17, 2022

JavaScript is a popular language that has numerous frameworks and libraries that make web development a lot easier. It's also the language that runs on the client-side, making it a desirable target for attackers. Cybersecurity threats and vulnerabilities on web applications are increasing. Therefore developers should craft secure web applications without compromising the user experience.

This guide presents the necessary steps to build secure web applications with JavaScript. Learn how to write secure JavaScript code that protects your web application from vulnerabilities and attacks.

Introduction

JavaScript is a programming language that allows web developers to add interactive features to web pages. When developers write JavaScript code and include them on a web page, their code is open to anyone. It means attackers can exploit it, steal user data or inject malicious scripts. JavaScript is designed to run on the client-side, which makes it a desirable target for attacks. This fact indicates that JavaScript developers must pay attention to security in their code.

1. Avoid Global Variables

Declaring variables as global lets any code access them, and potential attackers might exploit them. It's better to use block-scoped variables to reduce security risks.

// Bad
var x = 5;

// Good
let x = 5;

2. Prevent Cross-Site Scripting (XSS)

Cross-Site Scripting (XSS) attacks will inject malicious JavaScript code into web pages. The attacker might steal cookies or even use the victim's session to do other malicious activities. The easiest way to prevent it is to filter and sanitize user input. When taking user input in the form of text, ensure that the data sanitization on the server-side done properly.

// Bad
document.getElementById('output').innerHTML = userInput;

// Good
document.getElementById('output').textContent = userInput;

3. Prevent Code Injection

Code injection is the method of exploiting bugs in the code to execute arbitrary code. Sanitization and input validation is crucial here. Ensure that the user input doesn't contain any malicious data before executing it.

// Bad
eval('var input = ' + userInput + ';');

// Good
var input = JSON.parse(userInput);

4. Use HTTPS

When you send and receive data from the server, use HTTPS. Encrypting the data helps prevent others from viewing and manipulating data as it passes over the network. An attacker that can access data in transit can manipulate it, steal it, or inject additional JavaScript.

// Bad
const url = 'http://example.com/data.json';

// Good
const url = 'https://example.com/data.json';

5. Disable dangerous and unnecessary features

Many browsers and servers allow web developers to disable features that can be dangerous. It might be cross-domain requests, cookies, or inline scripts. Disabling unnecessary functionality could improve performance and decrease attack surfaces.

// Bad
res.setHeader('Access-Control-Allow-Origin', '*');
document.cookie = 'id=1; expires=Thu, 01 Jan 2037 00:00:00 UTC';

// Good
res.setHeader('Access-Control-Allow-Origin', 'https://example.com');

Conclusion

A secure website, application or software is a must-have to maintain user trust, and this guide provides a developer-friendly approach to write secure JavaScript code. We've seen several tips you can implement to improve the security of your web application easily. While it might seem like an additional task, investing time in cybersecurity will pay off in the long run. Knowledge of cybersecurity concepts is critical, and willingness to learn discloses many other techniques to secure web applications.