Senior LevelJavaScript & TypeScript
How does the Shadow Realm API and isolated JavaScript execution sandboxes work?
❓ Interview Prompt: Explain TC39 ShadowRealm proposal, isolated global scopes, code evaluation sandboxes, and security boundaries.
The ShadowRealm API (TC39 proposal) provides an isolated, synchronous JavaScript execution environment with its own distinct global object, standard built-in prototypes, and global scope.
Key Characteristics:
•
Scope Isolation: Code executed inside a ShadowRealm cannot access host global variables (
window or globalThis) or DOM elements.•
Primitive Value Communication: Values passed across the ShadowRealm boundary are restricted to primitive values and callable ShadowRealm functions.
•
Applications: Secure plugin systems, running untrusted user code, web-based code editors, micro-frontend isolation.
Code Implementation Example
javascript
// Initializing a ShadowRealm sandbox instance
// const realm = new ShadowRealm();
// Evaluate code securely inside isolated realm scope
// const result = await realm.importValue('./plugin.js', 'runPlugin');
// Executing code inside realm
// const sum = realm.evaluate('1 + 2');
console.log('ShadowRealm isolates globalThis and built-in prototypes from host scope.');💡Evaluating sandboxed plugin code inside isolated ShadowRealm global scope.
🎯 Interview Key Takeaway
ShadowRealm provides isolated global environments for executing plugins or untrusted code without risking host scope pollution.
#ShadowRealm#Sandboxing#Security#Senior
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