JavaScript Restrictor – Improve privacy by limiting web browser APIs

restrictor de javascript

JavaScript Restrictor – Improve privacy by limiting web browser APIs

JavaScript Restrictor is a cross browser extension from s0urce designed to improve user privacy by limiting access to web browser APIs that websites can use when running JavaScript. The extension is developed by Libor Pol? ák and several contributors, including Giorgio Maone, known for the NoScript extension. The development is supported by the European Commission’s Next Generation Internet Program.

The main goal of the project is to return some control to web browser users in regards to web browser APIs that can be abused by sites for user tracking and other invasive activities. The extension can block access to the APIs that it directly supports or manipulate the data that is provided to the sites.

Various websites collect information about users without their knowledge. The information collected is used to track users. Malicious websites can take fingerprints of users’ browsers or computers. JavaScript Restrictor protects the user by restricting or modifying various web browser APIs that are used to create side channels and identify the user, the browser or the computer. JavaScript Restrictor can block access to JavaScript objects, functions, and properties or provide a less precise implementation of its functionality, for example by modifying or falsifying values ​​returned by JS calls. The aim is to mislead the websites by providing false data or no data at all.

The extension modifies and restricts access to the web browser APIs. The list of supported APIs is available on the project’s GitHub web page. Includes HTMLCanvasElement, XMLHTTPRequest, ArrayBuffer, Geolocation API, WebWorker,, navigator.sendBeacon, WebGLRenderingContext, and others.

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Restrictor de JavaScript

JavaScript Restrictor is available for Mozilla Firefox, Google Chrome, and Opera, and it also works in other Chromium-based browsers such as Brave, Vivaldi, or Microsoft Edge.

Protection is divided into different levels, with level 2 being the default option for all visited websites. Options are provided to set different levels for sites.

  • Level 0: no protection
  • Level 1: minimum protection. Only major non-functionality changes apply
  • Level 2: recommended protection. More protections apply. Some sites can be broken.
  • Level 3: high level of protection. Full protections apply.

The full list of tier protections can be found on the project’s GitHub page. The Network Boundary Shield is enabled by default. It prevents web pages from using the browser “as a proxy between the local network and the public Internet.”

The protection encapsulates the WebRequest API, thus capturing all outgoing requests, including all elements created by JavaScript.

The JavaScript Restrictor extension adds an icon to the main browser toolbar after installation. Displays the current level of protection on the site and acts as a menu to change the level of that site on activation.

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privacy protection with javascript restriction

Just change the level to another value to set a different protection level for the active site. The network boundary shield can also be disabled for the site through the action menu.

Closing words

JavaScript Restrictor works in most modern web browsers. It improves user privacy by limiting access to certain browser APIs, which can be abused by tracking sites and other forms of attacks. Check the project website for more information on this.


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