Creating a Secure JavaScript Sandbox with ES6 Modules and globalThis

Mastering the globalThis in JavaScript for Secure Context Isolation

It is imperative to prevent unauthorized access to the global object when writing JavaScript code that interacts with external or untrusted inputs. This guarantees the security and consistency of your surroundings. One contemporary method of controlling global scope is via the object.

The object. Crucially, is reconfigurable, sandboxes or controlled execution environments can be made by temporarily overwriting it.

Developers can isolate code execution with this functionality, which is particularly useful when working with untrusted inputs. We can sandbox the code by establishing a unique global context, which will only permit access to a predetermined set of variables while preventing exposure to the remainder of the global object.

This article will discuss how to use and ES6 modules to construct a sandbox. I'll demonstrate a proof of concept that momentarily replaces the global context to guarantee safe code execution in a regulated setting.

Command	Example of Use
globalThis	myContext = globalThis; - is a unique object that offers a universal reference to the global object. Here, it's overwritten to emulate a sandbox and establish a unique global scope.
Proxy	let mySandbox = new Proxy(sandboxHandler, myContext); - AAn object's operations can be intercepted and redefined via a proxy; in this example, access to the sandbox context variables can be controlled.
get	get: (target, prop) => { ... } - The trap in the Proxy intercepts attempts to access properties of the sandbox object, ensuring that only allowed properties are returned, throwing errors for undefined ones.
finally	Lastly GlobalThis is equal to savedGlobal; - Whether an error occurs during execution or not, the block makes sure that the global object's integrity is maintained by restoring the original global context.
ReferenceError	'Property is not defined'; throw new ReferenceError; - A is thrown manually to handle cases where an attempt is made to access undefined variables within the sandbox, improving security by preventing unexpected access.
IIFE	((globalThis) => { ... })(globalThis); - An (Immediately Invoked Function Expression) is used to create a local scope, protecting the global object from unintended exposure while executing the sandboxed code.
try...catch	'Property is not defined'; throw new ReferenceError; - A is thrown manually to handle cases where an attempt is made to access undefined variables within the sandbox, improving security by preventing unexpected access.
savedGlobal	'Property is not defined'; throw new ReferenceError; - A is thrown manually to handle cases where an attempt is made to access undefined variables within the sandbox, improving security by preventing unexpected access.

Building a Secure Global Context with ES6 Modules and globalThis

The primary goal of the scripts that are offered is to provide a where the global object () is temporarily replaced. This method lets you keep important variables or properties from the original global object hidden, which is very helpful when working with external or untrusted code. Redefining the global scope ensures better control over variable access by essentially limiting the code to only access the properties declared in the sandbox.

Saving the original into a local variable () is the first step in the process in the first example. This is an important step because, once the sandboxed code is performed, the global context will be restored. Upon replacing the global context with a new object (here, ), the script endeavors to retrieve variables (here, a and ) situated within this sandbox. As demonstrated in the first issue mentioned, a reference error is raised if certain variables are not specified. Lastly, the block makes sure that, upon execution, the global context is always restored, avoiding any unexpected effects on other areas of the application.

The second approach makes use of a object to improve this procedure. In JavaScript, a proxy enables programmers to reinterpret and intercept actions taken on objects. Within this script, the Proxy monitors requests for property access and determines whether the desired property is present in the sandbox object. A is thrown in the event that the property cannot be located, guaranteeing that no external variables are accessible. Because of this, it is a strong option for securing the global scope and managing variable access in a dynamic sandbox setting.

In order to completely isolate the sandbox execution, the third script employs an IIFE (Immediately Invoked Function Expression). It is difficult for external code to access or interfere with the global context because the IIFE pattern wraps the entire action inside its own local scope. This method is more safe because the globalThis is not exposed to the outside world and is only altered within the IIFE. By guaranteeing that all sandboxed code operates in an entirely segregated environment, it enhances security and consistency in the script's operation.

let myContext = { a: 1, b: 2 };
let f = () => {
    let savedGlobal = globalThis;  // Save the original globalThis
    globalThis = myContext;        // Overwrite globalThis with the sandbox context
    try {
        let result = a + b;         // Attempt to access a and b within the sandbox
        return result;              // Return the calculated result
    } catch (e) {
        console.error(e);           // Catch errors, such as reference errors
    } finally {
        globalThis = savedGlobal;   // Restore the original global context
    }
};
console.log(f());

const myContext = { a: 1, b: 2 };
const sandboxHandler = {
    get: (target, prop) => {
        if (prop in target) {
            return target[prop];
        } else {
            throw new ReferenceError(\`Property \${prop} is not defined\`);
        }
    }
};
let mySandbox = new Proxy(myContext, sandboxHandler);
let f = () => {
    let savedGlobal = globalThis;
    globalThis = mySandbox;           // Overwrite with sandbox proxy
    try {
        let result = a + b;           // Access sandbox variables safely
        return result;
    } catch (e) {
        console.error(e);
    } finally {
        globalThis = savedGlobal;      // Restore global context
    }
};
console.log(f());

((globalThis) => {
    const myContext = { a: 1, b: 2 };
    const f = () => {
        let result = myContext.a + myContext.b;  // Access sandbox variables directly
        return result;
    };
    console.log(f());                // Log the result of the sandboxed function
})(globalThis);

Expanding the Use of Custom Global Context in JavaScript Sandboxing

Another benefit of employing in a sandboxing situation. In essence, you are rerouting the emphasis of your code to a controlled collection of variables when you overwrite the global object with a custom context, as demonstrated in our example. When running untrusted third-party scripts or separating distinct modules of a large online application, this strategy can be especially helpful in preventing cross-contamination of variables.

The fact that the ES6 module system in JavaScript has built-in scoping techniques that partially separate variables is another crucial element. On the other hand, using enables us to go beyond this. By preventing scripts that shouldn't be able to access it from seeing the original global context, this not only strengthens security but also helps prevent unintentional overwrites of global variables. This method works well for protecting apps from malicious or ill-written code.

Combining ES6 modules with improves security even further in situations where you need fine-grained control over which components of your application have access to the global object. By filtering access to specific properties within the global object, proxies let you make sure that only properties that are allowed can be accessed. The data of each tenant in a multi-tenant application needs to be completely segregated from the data of the other tenants. This solution is scalable and adaptable to various use cases.

1. What is the role of in JavaScript?
2. 'Property is not defined'; throw new ReferenceError; - A is thrown manually to handle cases where an attempt is made to access undefined variables within the sandbox, improving security by preventing unexpected access.
3. Why is sandboxing important in JavaScript?
4. Protecting sensitive variables, limiting unauthorized programs from accessing the global object, and isolating code execution are all made possible via sandboxing.
5. How does the object improve sandbox security?
6. A is an effective tool for sandbox environment security because it can intercept property accesses and limit access to only predefined properties.
7. How can an IIFE aid in the isolation of global contexts, and what does it mean?
8. An IIFE (Immediately Invoked Function Expression) encapsulates code execution, preventing external access to the global object and ensuring complete isolation of the sandbox.
9. An IIFE (Immediately Invoked Function Expression) isolates code execution, prohibiting external access to the global object and providing total isolation of the sandbox.
10. It is not recommended to utilize the deprecated statement. Contemporary substitutes such as and objects offer more reliable and safe options.