Optional assignment operator

[Darien Valentine]

> My thought was to have the following: this.foo ?= params?.foo; which can
be desugared to if (($ref = params?.foo) !== undefined) { this.foo = $ref; }

Are there any specific advantages to the new syntax you’re describing?
Initially, it appears to me like a less powerful form of an existing
syntactic feature — default initializers and binding patterns allow
expressing the same logic:

```
const obj = {
  demo(params={}) {
    ({ foo: this.foo=this.foo } = params);

    console.log(
      `params was ${ JSON.stringify(params) }; ` +
      `this.foo is now ${ JSON.stringify(this.foo) }`
    );
  }
}

obj.demo({ foo: 1 });
obj.demo({})
obj.demo({ foo: 2 });
obj.demo();
obj.demo({ foo: 3 });
obj.demo({});
```
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.mozilla.org/pipermail/es-discuss/attachments/20180704/80b6a6cc/attachment-0001.html>