Structural Validation with Proxy Traps

Snippet

Structural Validation with Proxy Traps

The Proxy object allows you to create a wrapper for another object, intercepting fundamental operations like property assignment. By using the 'set' trap and 'Reflect' API, you can implement robust runtime type checking.

snippet.js
javascript
const schema = { name: 'string', age: 'number' };
const handler = {
  set(target, prop, value) {
    if (schema[prop] && typeof value !== schema[prop]) {
      throw new TypeError(`Invalid type for ${prop}`);
    }
    return Reflect.set(...arguments);
  }
};
 
const user = new Proxy({}, handler);
user.name = 'Alice'; // Works
user.age = 'none';   // Throws TypeError

Breakdown

set(target, prop, value)

A trap for setting property values on the proxy object.

Reflect.set(...arguments)

Standard way to perform the default action of assigning a value to a property.

new Proxy({}, handler)

Constructs a proxy that uses the defined handler to intercept operations.

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Structural Validation with Proxy Traps

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