Client-Side Security

Input Validation

Goal: To prevent malicious or invalid data from being submitted to the server.

Methods:

• Regular Expressions: Use regular expressions to validate the format and content of user input.

  • Example:

    function validateEmail(email) {
                const emailRegex = /^[^\s@]+@[^\s@]+\.[^\s@]+$/;
                return emailRegex.test(email);
              }
              

  • Source: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Regular_Expressions

• HTML5 Input Validation: Utilize built-in HTML5 input validation attributes to enforce data types and patterns.

  • Example:

    <input type="email" name="email" required pattern="[a-z0-9._%+-]+@[a-z0-9.-]+\.[a-z]{2,}$" />
              

  • Source: https://developer.mozilla.org/en-US/docs/Learn/HTML/Forms/Introduction

• JavaScript Libraries: Leverage dedicated libraries such as validator.js for comprehensive input validation.

  • Example:

    const validator = require('validator');
              
              function validateUsername(username) {
                return validator.isAlphanumeric(username) && validator.isLength(username, { min: 3, max: 15 });
              }
              

  • Source: https://www.npmjs.com/package/validator

Error Handling

Goal: Gracefully handle errors that occur on the client-side to prevent unexpected behavior and enhance user experience.

Methods:

• Try-Catch Blocks: Use try-catch blocks to capture and handle exceptions.

  • Example:

    try {
                // Code that might throw an error
                const data = JSON.parse(userResponse);
              } catch (error) {
                console.error('Error parsing response:', error);
                // Display a user-friendly error message
              }
              

  • Source: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/try…catch

• Custom Error Classes: Define custom error classes to provide more specific error information.

  • Example:

    class InvalidInputError extends Error {
                constructor(message) {
                  super(message);
                  this.name = 'InvalidInputError';
                }
              }
              
              try {
                // Code that might throw an error
              } catch (error) {
                if (error instanceof InvalidInputError) {
                  // Handle invalid input specifically
                } else {
                  // Handle other types of errors
                }
              }
              

  • Source: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error

Secure Data Storage

Goal: Protect sensitive data from unauthorized access, modification, or disclosure.

Methods:

• Local Storage: Use Local Storage to store small amounts of data securely on the user’s device.

  • Example:

    localStorage.setItem('userToken', 'secret_token');
              

  • Source: https://developer.mozilla.org/en-US/docs/Web/API/Web_Storage_API

• Session Storage: Store data that is specific to the current browsing session.

  • Example:

    sessionStorage.setItem('cart', JSON.stringify(cartItems));
              

  • Source: https://developer.mozilla.org/en-US/docs/Web/API/Web_Storage_API

• IndexedDB: Use IndexedDB for storing larger amounts of structured data, such as user profiles or offline content.

  • Example:

    const request = indexedDB.open('myDatabase', 1);
              request.onsuccess = (event) => {
                const db = event.target.result;
                // Perform operations on the database
              };
              

  • Source: https://developer.mozilla.org/en-US/docs/Web/API/IndexedDB_API

Cross-Site Scripting (XSS) Protection

Goal: To prevent malicious scripts from being injected into the application and executed in the user’s browser.

Methods:

• Output Encoding: Encode all user-generated content before displaying it on the page.

  • Example:

    const username = 'John<script>alert("XSS")</script>';
              const encodedUsername = encodeURIComponent(username);
              // Display encodedUsername on the page
              

  • Source: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/encodeURIComponent

• Content Security Policy (CSP): Implement Content Security Policy (CSP) to restrict the resources that the browser is allowed to load.

  • Example:

    <meta http-equiv="Content-Security-Policy" content="script-src 'self' https://example.com">
              

  • Source: https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Content-Security-Policy