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Sandipan Roy
Sandipan Roy

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Securing User Input in JavaScript

Introduction User input is an integral part of web applications, and its essential to ensure that any input received from users is safe and secure. If user input is not validated and sanitized correctly, it can lead to vulnerabilities such as cross-site scripting (XSS) attacks and SQL injection attacks, which can put sensitive data at risk. In this blog, well explore how to secure user input in JavaScript by discussing input validation and sanitization techniques.

Input Validation

Input validation is the process of checking user input to ensure that it meets the expected format and data type. Validation can be done on the client-side or the server-side, but it's recommended to perform both for added security.

Client-Side Validation

Client-side validation is performed on the user's browser and provides immediate feedback to the user. It's useful for validating input format, such as checking if an email address is in the correct format or if a password meets the minimum length requirement. However, client-side validation should not be relied on for security purposes, as it can be bypassed by attackers.

Server-Side Validation

Server-side validation is performed on the server-side and ensures that input data is valid and safe to use. Server-side validation can detect and prevent security vulnerabilities such as SQL injection attacks and cross-site scripting attacks. It's crucial to validate user input on the server-side to prevent security vulnerabilities.


Input sanitization is the process of cleaning user input to remove any potentially malicious code. Sanitization is often used in combination with validation to provide an added layer of security. It's important to note that sanitization should not be relied on solely for security, as it's not always possible to remove all malicious code.

Sanitizing User Input

in JavaScript JavaScript provides several methods for sanitizing user input, including:

  • .replace() Method:


const userInput = "<script>alert('Hello World!')</script>";
const sanitizedInput = userInput.replace(/[<>]/g, '');
console.log(sanitizedInput); // Output: "scriptalert('Hello World!')/script"

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  • .trim() Method:


const userInput = " Hello World! ";
const sanitizedInput = userInput.trim();
console.log(sanitizedInput); // Output: "Hello World!"

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  • .escape() Method:


const userInput = "<script>alert('Hello World!')</script>";
const sanitizedInput = escape(userInput);
console.log(sanitizedInput); // Output: "%3Cscript%3Ealert('Hello%20World!')%3C/script%3E"

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Securing user input in JavaScript is critical for protecting sensitive data and preventing security vulnerabilities. Input validation and sanitization are essential techniques for securing user input. It's important to perform both client-side and server-side validation and use appropriate sanitization techniques to prevent XSS attacks and other security vulnerabilities. By following these best practices, developers can ensure their applications are secure and provide a safe user experience.


  1. OWASP. (2022). Input Validation Cheat Sheet.

  2. OWASP. (2022). Cross-Site Scripting (XSS) Prevention Cheat Sheet.

  3. MDN Web Docs. (2022). String.prototype.replace().

  4. MDN Web Docs. (2022). String.prototype.trim().

  5. MDN Web Docs. (2022). escape().

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