[[Enumerate]] in JS code

enumerate.js

function *enumerate(obj) { 
  if (Object(obj)!==obj) return  undefined;
  let visited = new Set;  
  while (obj!==null ) {
    for (name of Object.getOwnPropertyNames(obj)) { 
      if (!visited.has(name)) {
        let desc = Object.getOwnPropertyDescriptor(obj,name);
        if (desc) {
          visited.add(name);
          if (desc.enumerable) yield name;
        }
      }
    }                                                           
    obj = Object.getPrototypeOf(obj);
  }
}