Synthesizing Members Directly on an Instance

The two pillars

Rather than calling proxy.key, we should be able to perform anyInstanceOfMap.key. To achieve this, we need to bring two different pieces of knowledge together.

1. First, when a nonexistent property is requested on an object, JavaScript automatically requests it from the object’s prototype. If the prototype does not have it, the search continues through the prototype chain—see Understanding Prototypal Inheritance.

2. Second, a proxy can trap requests ...