Array destructuring assignment not working in v8 with harmony option in Node.js

Question

I want to learn how to enable harmony v8 options in Node, and my node version is:

$ node -v                                                                      
v5.5.0

Use ES6 destructuring as an example for testing

$ cat destructure.js
'use strict'
var a, b
[a, b]  = [1, 2] 
console.log(a, b)

Run it straight gets error as expected.

$ node destructure.js 
/usr/home/mko_io/pure-js-files/destructure.js:3
[a, b]  = [1, 2]
^^^^^^

But get the same error, after the flag has been set:

$ node --harmony_destructuring destructure.js 
/usr/home/mko_io/pure-js-files/destructure.js:3
[a, b]  = [1, 2]
^^^^^^

ReferenceError: Invalid left-hand side in assignment

Where did I do it wrong?

score 2 · Accepted Answer · edited May 23 '17 at 12:22

2

Apparently this is/was a bug in the V8 JavaScript engine.

'use strict'
var a, b
[a, b]  = [1, 2] 
console.log(a, b)

Does not work but...

'use strict'
var [a, b]  = [1, 2] 
console.log(a, b)

does work, when using the --harmony_destructuring.

Looks like the experimental feature is not yet fully spec-compliant.

The relevant bug report for V8 marked this issue as fixed in December 2015, so now we just need to wait for the updated V8 to make it into Node. @mscdex has informed me this fix will be available in Node v6.0.0.

edited May 23 '17 at 12:22

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answered Mar 18 '16 at 05:39

Alexander O'Mara

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It already works in node master and thus will be in the upcoming node v6.0.0. – mscdex Mar 18 '16 at 05:49
Thank you Alex, I thought enabling the v8 flag could enable me to learn the new feature easy comparing to testing in browser. – mko Mar 20 '16 at 02:42
1

Nit: it wasn't a bug, it's just that despite looks, destructuring (binding) and destructuring _assignment_ are entirely separate features (in terms of both language spec and implementation), and V8 shipped the former first. The latter followed behind the `--harmony-destructuring-assignment` flag. – Andreas Rossberg Apr 05 '16 at 18:21
Or you can upgrade to Node 6.5v – Gaurav Gandhi Sep 08 '16 at 04:39

score 1 · Answer 2 · edited May 23 '17 at 12:22

1

Destructure is broken.

In progress features can be activated individually by their respective harmony flag (e.g. --harmony_destructuring), although this is highly discouraged unless for testing purposes.

https://nodejs.org/en/docs/es6/ and this answer Destructuring in Node.JS

edited May 23 '17 at 12:22

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answered Mar 18 '16 at 05:46

Deepak Puthraya

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Array destructuring assignment not working in v8 with harmony option in Node.js

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