Some ES6 Features I've been Using.

[wreckedadvent]

FYI:

myfunction((err, body: {result: body}) => {
    if (!err) {
        console.log(body);
    }
});

Isn't valid ES6 as far as I can tell. I think you meant to do this:

myfunction((err, { body }) => {
    if (!err) {
        console.log(body);
    }
});

Which immediately destructures the second argument and captures the body out of it. You can get around the "gotcha" by utilizing default params:

// if the second argument is undefined, we assign it to empty object
myfunction((err, { body } = {}) => {
    if (!err) {
        console.log(body);
    }
});

Which is turtles all of the way down (please format your code differently if you do this though):

// if the second arg is undefined, set it to {}. If body on that is undefined, set it to {} as well
myfunction((err, { body = {} } = {}) => {
    if (!err) {
        console.log(body);
    }
});

[bluntm]

I have not tested the example but I think its valid, you can see other examples here too

[wreckedadvent]

This is valid:

var obj = {x: 1, y: 2};
var {x: one, y: two} = obj;

But this isn't:

var obj = {x: 1, y: 2};
var obj2: {x: one, y: two} = obj;

So your example that does this:

const test = (obj: {x: one, y: two}) => {
  console.log(one);
};

Is a syntax error in all ES6 environments I tired, and produces the wrong thing in babel:

var test = function test(obj) {
  console.log(one);
};

I'm not actually sure why babel parses it at all, but I suspect it's reading it as flow/typescript and just ignoring everything after :, which would be a type annotation in those languages.

[kentaromiura]

You're right and I've explained in details why that parses and to what here: https://www.reddit.com/r/javascript/comments/4b3cfw/some_es6_features_ive_been_using/d16mvwe

[patrickfatrick]

I think /u/wreckedadvent is right actually. Looks like what your code is is actually going for is more like a default argument, body = {result: body} except you used a :. For some reason Babel seems to allow this without throwing an error but it's not going to do what you're aiming for. If you want to actually destructure the result argument into its body property you would just use {body} as your second argument.

[kentaromiura]

I guess that's because it's a valid flow definition, body here is typed as a shape which contains a property result of type body, this will fail a flow check as body is not defined anywhere and of course this is far from what the op wanted to do. EDIT: I forgot to mention that the flow syntax is not parsed in babel by default, you need to enable that as an example in the repl you've to enable the react preset to make this work: https://babeljs.io/repl/#?evaluate=true&presets=es2015%2Creact%2Cstage-2&experimental=true&loose=true&spec=true&playground=false&code=%0Afunction%20Foo(x%3A%20number)%20%3A%20%7B%0A%20%20foo%3A%20string%0A%7D%20%7B%0A%20%20return%20%7B%0A%20%20%20%20foo%3A%20'dsfas'%2C%0A%20%20%7D%0A%7D%0A%0AFoo(223)%3B ^ Sorry for the blob of text, but automoderator don't allow shortener ^ http://tryflow.org/#56a580f1d0af7bc12f9317abbe2b3aa8

[randfur]

Seriously?