Implement strictdynamic in scriptcources in app.use

As of my last update in September 2021, there is no standard directive called strictdynamic in the Content Security Policy (CSP) specification. However, CSP provides several directives that help improve web application security, and one of them is strict-dynamic.

The strict-dynamic directive allows the execution of JavaScript code loaded from a whitelisted domain and disallows any inline scripts or the use of the eval() function. This helps mitigate the risk of cross-site scripting (XSS) attacks by limiting the execution of dynamically generated scripts to specific trusted sources.

To implement strict-dynamic in your application using Express.js and the helmet middleware (which helps set security-related HTTP headers, including CSP), you can follow these steps:

  1. Install the required packages:
npm install express helmet

Set up your Express application and use the helmet middleware:

const express = require('express');
const helmet = require('helmet');

const app = express();

// Use the helmet middleware

// ... Your other middleware and routes ...

// Handle CSP header
app.use((req, res, next) => {
  // Define the CSP header with strict-dynamic
  const cspDirective = "default-src 'self'; script-src 'strict-dynamic' 'self';";
  res.setHeader('Content-Security-Policy', cspDirective);

// ... Other app configurations ...

// Start the server
const port = 3000;
app.listen(port, () => {
  console.log(`Server listening on port ${port}`);

In the above code, we use helmet() middleware to set various security-related headers, including the Content-Security-Policy (CSP) header. The CSP header is set in the subsequent middleware function, where we specify the strict-dynamic directive as part of the script-src directive. This allows scripts to be executed only from the whitelisted domain “” and disallows any inline scripts or the use of eval().

Please note that the syntax and functionality of CSP may change over time, so it’s essential to check the latest documentation and CSP specification for updates and best practices. As of my last update, strictdynamic was not part of the standard, and it is recommended to use strict-dynamic as shown above.