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?

Answer 1

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.