Is it possible to destructure onto an existing object? (Javascript ES6)

Question

While ugly and a bit repetitive, you can do

({x: oof.x, y: oof.y} = foo);

which will read the two values of the foo object, and write them to their respective locations on the oof object.

Personally I'd still rather read

oof.x = foo.x;
oof.y = foo.y;

or

['x', 'y'].forEach(prop => oof[prop] = foo[prop]);

though.

IMO this is the easiest way to accomplish what you're looking for:

let { prop1, prop2, prop3 } = someObject;
let data = { prop1, prop2, prop3 };

  // data === { prop1: someObject.prop1, ... }

Basically, destructure into variables and then use the initializer shorthand to make a new object. No need for Object.assign

I think this is the most readable way, anyways. You can hereby select the exact props out of someObject that you want. If you have an existing object you just want to merge the props into, do something like this:

let { prop1, prop2, prop3 } = someObject;
let data = Object.assign(otherObject, { prop1, prop2, prop3 });
    // Makes a new copy, or...
Object.assign(otherObject, { prop1, prop2, prop3 });
    // Merges into otherObject

Another, arguably cleaner, way to write it is:

let { prop1, prop2, prop3 } = someObject;
let newObject = { prop1, prop2, prop3 };

// Merges your selected props into otherObject
Object.assign(otherObject, newObject);

I use this for POST requests a lot where I only need a few pieces of discrete data. But, I agree there should be a one liner for doing this.

EDIT: P.S. - I recently learned you can use ultra destructuring in the first step to pull nested values out of complex objects! For instance...

let { prop1, 
      prop2: { somethingDeeper }, 
      prop3: { 
         nested1: {
            nested2
         } 
      } = someObject;
let data = { prop1, somethingDeeper, nested2 };

Plus, you could use spread operator instead of Object.assign when making a new object:

const { prop1, prop2, prop3 } = someObject;
let finalObject = {...otherObject, prop1, prop2, prop3 };

Or...

const { prop1, prop2, prop3 } = someObject;
const intermediateObject = { prop1, prop2, prop3 };
const finalObject = {...otherObject, ...intermediateObject };

No, destructuring does not support member expressions in shorthands but only plain propertynames at the current time. There have been talks about such on esdiscuss, but no proposals will make it into ES6.

You might be able to use Object.assign however - if you don't need all own properties, you still can do

var foo = …,
    oof = {};
{
    let {x, y} = foo;
    Object.assign(oof, {x, y})
}

Other than Object.assign there is the object spread syntax which is a Stage 2 proposal for ECMAScript.

    var foo = {
      x: "bar",
      y: "baz"
    }
    
    var oof = { z: "z" }
    
    oof =  {...oof, ...foo }
    
    console.log(oof)

    /* result 
    {
      "x": "bar",
      "y": "baz",
      "z": "z"
    }
    */

But to use this feature you need to use stage-2 or transform-object-rest-spread plugin for babel. Here is a demo on babel with stage-2

BabelJS plugin

If you are using BabelJS you can now activate my plugin babel-plugin-transform-object-from-destructuring (see npm package for installation and usage).

I had the same issue described in this thread and for me it was very exhausting when you create an object from a destructuring expression, especially when you have to rename, add or remove a property. With this plugin maintaining such scenarios gets much more easier for you.

Object example

let myObject = {
  test1: "stringTest1",
  test2: "stringTest2",
  test3: "stringTest3"
};
let { test1, test3 } = myObject,
  myTest = { test1, test3 };

can be written as:

let myTest = { test1, test3 } = myObject;

Array example

let myArray = ["stringTest1", "stringTest2", "stringTest3"];
let [ test1, , test3 ] = myArray,
  myTest = [ test1, test3 ];

can be written as:

let myTest = [ test1, , test3 ] = myArray;

It's totally possible. Just not in one statement.

var foo = {
    x: "bar",
    y: "baz"
};
var oof = {};
({x: oof.x, y: oof.y} = foo); // {x: "bar", y: "baz"}

(Do note the parenthesis around the statement.) But keep in mind legibility is more important than code-golfing :).

Source: http://exploringjs.com/es6/ch_destructuring.html#sec_assignment-targets

You can just use restructuring for that like this:

const foo = {x:"a", y:"b"};
const {...oof} = foo; // {x:"a", y:"b"} 

Or merge both objects if oof has values:

const foo = {x:"a", y:"b"};
let oof = {z:"c"}
oof = Object.assign({}, oof, foo)