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Sanitize Input Javascript: Javascript Explained

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Sanitizing input in Javascript is an essential step of any web development process, as it helps protect application users from malicious input attacks. When sanitizing input, developers are ensuring that user data is sanitized before being received, handled, or stored by a program. In this article, we will be discussing what sanitize input is, the benefits of sanitizing input in Javascript, and some tools for implementing and detecting unsanitized input in your existing codebase.

What is Sanitize Input Javascript?

Sanitizing input in Javascript is a process of cleaning and validating user-inputed data. This includes ensuring that data is formatted correctly, removing any malicious code, and eliminating any errors from being entered. It also includes checking for malicious scripts and other forms of attack vectors. Sanitizing data is important for security and the stability of an application, as a malicious input can have severe impacts, such as leaking private user data or crashing the system.

In addition to the security benefits, sanitizing input can also improve the user experience. By validating user input, applications can provide more accurate feedback and prevent users from entering invalid data. This can help reduce frustration and improve the overall user experience.

Benefits of Sanitizing Input in Javascript

Sanitizing input in Javascript has countless benefits, including enhanced security, performance, usability, and robustness. By sanitizing input, developers are better protected against malicious inputs, denied services attacks, and errors in their code. It also makes the application overall more stable and secure, as unanticipated events are no longer likely to occur. Additionally, sanitized input can help to improve your application’s performance by eliminating errors and preventing malicious attacks.

Sanitizing input also helps to improve the user experience by ensuring that the data entered is valid and consistent. This helps to reduce the amount of time spent debugging and troubleshooting, as well as reducing the risk of data loss or corruption. Furthermore, sanitizing input can help to improve the overall robustness of the application, as it ensures that the data is always valid and consistent.

How to Implement Sanitization in Javascript

Implementing sanitize input in Javascript can be done in several different ways. The simplest implementation is to always escape user input before it is processed by your application. Escaping user input is a process used to limit the potential for malicious inputs to be sent to your application. Additionally, you can use the HTML encode and decode functions – which convert a string of characters into the appropriate HTML code – to reduce the potential for malicious inputs.Depending on your use case, the way you sanitize might differ. Here’s how to implement basic sanitization in JavaScript for a few common scenarios

1. Sanitizing Input to Protect Against Cross-Site Scripting (XSS):

If you’re inserting user input into the DOM, you should avoid using methods like innerHTML which can execute arbitrary JavaScript. Instead:

Use textContent to safely insert text into the DOM:

let userInput = "<script>alert('XSS');</script>";
document.getElementById("output").textContent = userInput;

If you must insert HTML, consider using a library like DOMPurify to sanitize the input:

let sanitizedHTML = DOMPurify.sanitize(userInput);
document.getElementById("output").innerHTML = sanitizedHTML;

2. Sanitizing Input for Database Storage:

If you’re interacting with a database, especially SQL-based ones, you must guard against SQL injection attacks. While parameterized queries are the best solution, for JavaScript-side sanitization:

  1. Avoid constructing SQL queries by concatenating strings with user input.
  2. Use libraries or frameworks that provide parameterized query support.

3. Sanitizing URLs:

If you’re taking URLs as input and redirecting or making requests based on those URLs, ensure they are safe.

function sanitizeURL(url) {
   let a = document.createElement('a');
   a.href = url;
   return a.protocol + "//" + + a.pathname + + a.hash;

4. Sanitizing JSON:

If you’re accepting JSON input, always parse it with the native JSON.parse method, which will prevent the execution of arbitrary JavaScript..

try {
   let data = JSON.parse(userInput);
} catch (e) {
   console.error("Invalid JSON input:", e);

Common Examples of Sanitizing Input in Javascript

Sanitizing user input in Javascript is a common practice amongst developers. Here are some of the most common methods used to sanitize user input:

  • Validation – validating user input to ensure it meets a set of parameters.
  • Input sanitation – eliminating any malicious or invalid characters that may be contained within the user’s input.
  • Input encoding – encoding the user’s input into an accepted format before sanitization.
  • Input filtering – filtering out any malicious content from the user’s input before it can be accessed.

It is important to note that these methods should be used in combination with one another to ensure the highest level of security. Additionally, developers should also consider using a third-party library to help with sanitizing user input, as this can help to reduce the amount of time and effort spent on manual sanitization.

Potential Security Risks of Not Sanitizing Input

Failing to sanitize user input can have disastrous consequences for your application, as it opens the door for malicious inputs to be processed by your application. These malicious inputs could result in confidential data being stolen, denial of service attacks, or other forms of exploitation. Therefore, it’s critical to sanitize user input before processing or storing it.

Sanitizing user input involves validating the data to ensure it meets certain criteria, such as being of the correct type, length, and format. It also involves filtering out any potentially malicious content, such as HTML tags, JavaScript code, and SQL queries. By taking these steps, you can ensure that your application is secure and protected from malicious attacks.

Best Practices for Writing Secure Code in Javascript

Writing secure code in Javascript is essential for any application’s security. Here are some best practices for writing secure code:

  • Sanitize all user input before processing or storing it.
  • Never trust user-inputted data – always validate and filter it.
  • Always use a secure connection when requesting or transmitting user data.
  • Encode all user input correctly before processing or storing it.
  • Use libraries such as DOMPurify to filter malicious content from user input.

It is also important to use secure authentication methods such as two-factor authentication and to use secure passwords. Additionally, it is important to keep your code up to date with the latest security patches and to use secure coding practices such as avoiding the use of global variables and using secure coding libraries.

Tools for Detecting Unsanitized Inputs in Javascript

Detecting unsanitized inputs in your code can be a tricky process, as they are often hard to spot unless you already know what to look out for. Luckily, there are numerous tools available that make detecting unsanitized inputs easier. These tools can detect malicious inputs, validate user input, and even scan your source code for suspicious behaviour.

One of the most popular tools for detecting unsanitized inputs is the OWASP Zed Attack Proxy (ZAP). ZAP is an open-source tool that can detect and alert you to any potential security vulnerabilities in your code. It can also be used to scan your source code for any malicious inputs, and can even be used to test your code against a variety of attack scenarios. Additionally, ZAP can be used to detect and block any malicious requests that are sent to your application.


Sanitizing user input is an essential step for any web development process. By sanitizing user input in Javascript, developers are able to minimize the risk of malicious inputs being processed, as well as improving the stability and performance of their application. Furthermore, there are numerous tools available that make detecting unsanitized inputs easier. Knowing these things is essential for developing secure applications.

It is important to remember that sanitizing user input is only one part of the security process. Developers should also ensure that their applications are regularly tested for vulnerabilities, and that they are using the latest security protocols. Additionally, developers should be aware of the potential risks associated with user input, and take steps to mitigate them.

Anand Das

Anand Das

Anand is Co-founder and CTO of Bito. He leads technical strategy and engineering, and is our biggest user! Formerly, Anand was CTO of Eyeota, a data company acquired by Dun & Bradstreet. He is co-founder of PubMatic, where he led the building of an ad exchange system that handles over 1 Trillion bids per day.

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