Managing Private State with WeakMap

Snippet

Managing Private State with WeakMap

WeakMap is a collection of key/value pairs in which the keys are objects and are weakly referenced. This is an intermediate pattern for creating truly private state in JavaScript classes before the native '#' syntax was widely adopted, and it ensures that private data is garbage collected when the instance is destroyed.

snippet.js
javascript
const privateData = new WeakMap();
 
class SecureUser {
  constructor(name, token) {
    privateData.set(this, { name, token });
  }
 
  getProfile() {
    const { name } = privateData.get(this);
    return `User: ${name}`;
  }
}
 
const user = new SecureUser('Alice', 'secret-123');
console.log(user.token); // undefined

Breakdown

const privateData = new WeakMap();

Creates a map where keys (objects) do not prevent garbage collection.

privateData.set(this, { name, token });

Stores sensitive data associated with the current instance ('this') outside the object itself.

privateData.get(this);

Retrieves the stored private data using the current instance as the lookup key.

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Managing Private State with WeakMap

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