Destructuring of arrow function arguments via computed property throws in v6.x

[oaleynik]

• node -v: v6.x
• uname -a: Darwin Olegs-MacBook-Pro.local 16.4.0 Darwin Kernel Version 16.4.0: Wed Dec 7 12:06:26 PST 2016; root:xnu-3789.41.1~5/RELEASE_X86_64 x86_64

// Throws in Nodejs 6.x with -> ReferenceError: y is not defined
var y = 'a';
var g20 = ({[y]: x}) => { var y = 'b'; return x; };
require('assert').equal(1, g20({a: 1, b: 2}));

The test case is taken from: https://github.com/nodejs/node/blob/v6.x/deps/v8/test/mjsunit/es6/destructuring.js#L893

[vsemozhetbyt]

According to node.green it should work in 6.9.0–6.9.2. This example from "computed properties" tooltip there works fine in the 6.9.2

function test(){
  var qux = "corge";
  return function({ [qux]: grault }) {
    return grault === "garply";
  }({ corge: "garply" });
}

console.log(test());

[oaleynik]

@vsemozhetbyt example from node.green indeed works. But the same example, slightly changed, throws:

const qux = "corge";
const fn = ({ [qux]: grault }) => {
  return grault === "garply";
};

console.log(fn({ corge: "garply" }));

UPDATE: What is interesting - if replace arrow function with the regular function - it works.

[vsemozhetbyt]

So this is corrected formulation: destructuring of arrow function arguments via computed property throws in the Node.js 6.9.2:

// does not throw in the Node.js 6.9.2
const obj = { key: 'value' };

const keyComputed = 'key';

function fn({ [keyComputed]: param }) {}

fn(obj);

// throws in the Node.js 6.9.2
const obj = { key: 'value' };

const keyComputed = 'key';

const fn = ({ [keyComputed]: param }) => {};

fn(obj);

[oaleynik]

Thanks @vsemozhetbyt, I've updated the issue title and description.

[vsemozhetbyt]

It seems the bug is actual only for destructuring. Other evaluations in the parameters scope are OK.

// does not throw in the Node.js 6.9.2
const obj = { key: 'value' };

const keyComputed = 'key';

function fn(param = obj[keyComputed]) { console.log(param); }

fn();

// does not throw in the Node.js 6.9.2
const obj = { key: 'value' };

const keyComputed = 'key';

const fn = (param = obj[keyComputed]) => { console.log(param); };

fn();

[oaleynik]

I see the test case for this in V8 on 6.x branch: https://github.com/nodejs/node/blob/v6.x/deps/v8/test/mjsunit/es6/destructuring.js#L893

Should not it fail?

[vsemozhetbyt]

Well, this throws:

// throws in the Node.js 6.9.2
var y = 'a';
var g20 = ({[y]: x}) => { var y = 'b'; return x; };
require('assert').equal(1, g20({a: 1, b: 2}));

I don't know why it does not fail there(

[vsemozhetbyt]

Maybe these tests are not actually tested during Node.js build (unlike Node tests)?

[MylesBorins]

the V8 tests are not run during the normal node CI

…

On Mon, Dec 19, 2016, 7:50 PM Vse Mozhet Byt ***@***.***> wrote: Maybe these tests are not actually tested during Node.js build (unlike Node tests <https://github.com/nodejs/node/tree/master/test>)? — You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHub <#10347 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AAecV_qmc70Sg0sn2EgYzPqz3CeYCqAhks5rJyZdgaJpZM4LRRZ2> .