ES6 Structuring Assignment?

Question

The new destructuring assignment features of ES6 are fairly well known now (live copy on Babel\'s REPL); in the case of variables that already exist:

Answer 1

The closest I've come up with is to use Object.assign and a temporary object (live copy):

let a = "a", b = "b";             // The variables
let obj = {c: "c"};               // The existing object
Object.assign(obj, {a, b});       // "Structuring" assignment, sort of
console.log(JSON.stringify(obj)); // "{"c":"c","a":"a","b":"b"}

It's fairly simple, but it's a function call and a temporary object.

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Update: Bergi points out in a comment that there's a strawman proposal (link now dead) for a := operator that will do this, and one of their first use cases is indeed the use case that primarily lead me to this question: Constructors:

// From strawman proposal linked above, doesn't actually exist yet!
class Point {
   constructor(x,y) {
      this := {x,y}  //define and initialize x and y properties of new object
      //   ^^
   }
}

So given that strawman exists, I suspect for now the assign is going to be the best I can do in ES6. The old wiki with the strawman is offline, and there's nothing about := in the proposals repo.