Professional JavaScript for Web Developers, 4th Edition

9Proxies and Reflect

WHAT'S IN THIS CHAPTER?

• Proxy fundamentals
• Proxy traps and reflect methods
• Proxy patterns

Freshly introduced in ECMAScript 6, proxies and reflection are totally new constructs that afford you the ability to intercept and shim additional behavior into fundamental operations within the language. More specifically, you can define a proxy object associated with a target object, and the proxy object can be used as an abstracted target object within which you can control what happens when various operations are performed before they actually reach the target object.

For developers approaching this subject for the first time, this is a fairly nebulous concept paired with a healthy corpus of new terminology. Working through multiple examples will help to cement your understanding.

NOTE   There is no analogue for proxies in ECMAScript versions prior to ES6. Because it is a fundamentally new language ability, many transpilers are unable to convert proxy behavior into earlier ECMAScript versions because replicating the behavior of a proxy is effectively impossible. Therefore, proxies and reflection are useful only in situations where native support is offered on 100 percent of platforms. It is possible to detect support for proxies and divert to fallback code as necessary, but this would lead to code duplication and is therefore discouraged.

PROXY FUNDAMENTALS

As mentioned in the chapter introduction, a proxy behaves as an abstraction for a target object. ...