Clean way to keep original variable and destructure at the same time

One possible way:

const result = doSomething(), 
    { a, b } = result;

You still have to duplicate the name, though. const token isn't quite right-handy. )

Idea 1

Create this helper function:

function use(input, callback) {
    callback(input, input);
}

and use it like:

use(doSomething(), (result, {a, b}) => {
    // Do something with result as a whole, or a and b as destructured properties.
});

For example:

use ({a: "Hello", b: "World", c: "!"}, (result, {a, b}) => {
  console.log(result);
  console.log(a);
  console.log(b);
});

// generates
// {a: "Hello", b: "World", c: "!"}
// Hello
// World

They're not const, but they're scoped, for better or worse!

---

Idea 2

Combine array and object deconstruction. Create this helper function:

const dup = input => [input, input];

And then deconstruct away like so:

const [result, {a, b}] = dup(doSomething());

Now, your result, a, and b are all consts.