JavaScript security best practices for building secure applications

To safeguard applications from vulnerabilities and potential threats, secure coding practices are indispensable. The goal isn't solely to ensure the functional accuracy of the code but also to guarantee its security, ensuring users enjoy a safe and uninterrupted experience. 

JavaScript security best practices

This comprehensive checklist offers developers a detailed set of secure coding guidelines specifically tailored for JavaScript, each elucidated with practical examples. When undertaking a security code review, it becomes paramount for developers not only to understand but also to rigorously ensure that these established best practices are consistently followed.

1. Avoiding Eval()

The _`eval()` function evaluates a string as JavaScript code. This can be dangerous if the string contains malicious code.

Example:

Avoid this:

     eval('alert("Hello World")');

Instead, find safer alternatives to achieve the desired functionality.

‍

2. Validating and Sanitizing Input

Always validate and sanitize user input to prevent cross-site scripting (XSS) and other injection attacks.

Example:

     // the input string
     const userInput = ""; 
     
     // sanatize the input string before use
     const sanitizedInput = userInput.replace(/.*?<\/script>/gi, ''); 
     
     document.getElementById('output').innerText = sanitizedInput;

‍

3. Using Content Security Policy (CSP)

CSP helps prevent XSS attacks by controlling which resources can be loaded.

Example:

     Content-Security-Policy: default-src 'self';

4. Avoiding Inline Event Handlers

Inline event handlers can be a vector for XSS attacks.

Example:

Avoid this:

_{<button onclick="doSomething()">Click me</button>}

‍

Instead, use:

_{<button id="myButton">Click me</button>
<script>
  document.getElementById('myButton').addEventListener('click', doSomething);
</script>}

‍

5. Using HTTPS

Always use HTTPS to ensure data integrity and confidentiality.

Example:

     if (window.location.protocol !== "https:") {
       window.location.protocol = "https:";
     }

‍

6. Avoiding Direct DOM Manipulation

Directly manipulating the DOM can introduce XSS vulnerabilities.

Example:

Avoid this:

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

Instead, use:

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

‍

7. Securing Cookies

Use the _`HttpOnly`, _`Secure`, and _`SameSite` attributes to enhance cookie security.

Example:

     document.cookie = "sessionId=12345; Secure; HttpOnly; SameSite=Strict";

8. Avoiding Global Variables

Global variables can be modified by other scripts, leading to potential security issues.

Example:

Avoid this:

     var globalVar = "value";

Instead, use:

     (function() {
       var privateVar = "value";
     })();

‍

9. Using Modern JavaScript Features

Modern JavaScript features like _`let`, _`const`, and arrow functions can help reduce the risk of certain vulnerabilities.

Example:

     const secureFunction = (input) => {
       // Process input securely
     };

‍

10. Keeping Libraries Updated

Outdated libraries can have known vulnerabilities. Regularly update your libraries to their latest versions.

Example:

     npm update

Remember, security is a multi-faceted concern, and while these practices can help, they are just a starting point. Regularly review your code, stay updated on application security best practices, and consider using tools like linters and security scanners to identify potential vulnerabilities.

‍