Unlock JavaScript’s Power: How to Use Proxy for Validation, API Calls & More

Proxy is a lesser‑known but powerful JavaScript object that can be used for type checking, data validation, monitoring asynchronous functions, and wrapping RESTful services.

Proxy are magic methods

Proxy is a JavaScript object that can wrap another object or function, monitoring the wrapped target without needing to know whether the target exists. It is similar to metaprogramming features in other languages.

Three key concepts

Targets : the object or function being proxied.

Handler : the object that defines traps for the target.

Traps : functions that intercept operations on the target (see more at the linked article).

Defining a Proxy

In ES6 a Proxy is created with new Proxy(target, handler). The target is the original object, and the handler supplies trap functions that customize behavior.

For example, a simple target object with a message property and a handler with a get trap can be used to intercept property access.

Using Proxy for validation

A Proxy can validate property values by defining a set trap. The following diagram shows an empty object as the target and a handler that checks values before assignment.

Wrapping RESTful API calls

By combining axios with a Proxy, you can create an API client. A baseURL is used to configure an axios instance, and the handler’s get trap returns an object containing get, post, put, delete, and patch methods. The proxy is applied to an empty object, allowing you to call api.get(...) etc.

Conclusion

Proxies can be employed for validation, correcting property values, tracking property access, warning about unknown properties, handling array indices, data binding, accessing RESTful services, dereferencing, monitoring asynchronous functions, type checking, and more. See the linked ES6 proxy guide for additional use‑cases.

The author plans to publish a series of follow‑up articles.

Note: the code examples can still be further optimized.