Destructuring in Node.JS

Question

This recent video claims that EMCAScript 6 destructuring is already partially implemented in Node.JS. I have tried various examples (using v0.10.12 and the --harmony flag), such as

var [a, b] = [1, 2];

and

var {a: a, b: b} = {a: 1, b: 2};

to no avail. This ticket seems to suggest that destructuring is not yet supported in V8.

Is destructuring really partially implemented in Node.JS? What are snippets of code I can play with?

mikemaccana · Accepted Answer · 2017-01-16 14:43:52Z

91

Update for node v6 and newer: Node v6 supports destructuring assignment without anything special needed:

var [a, b] = [1, 2];

For older versions of node: You can get the list of supported harmony features by typing:

node --v8-options | grep harmony

node 5.x will give you:

--es_staging (enable all completed harmony features)
--harmony (enable all completed harmony features)
--harmony_shipping (enable all shipped harmony fetaures)
--harmony_modules (enable "harmony modules" (in progress))
--harmony_regexps (enable "harmony regular expression extensions" (in progress))
--harmony_proxies (enable "harmony proxies" (in progress))
--harmony_sloppy_function (enable "harmony sloppy function block scoping" (in progress))
--harmony_sloppy_let (enable "harmony let in sloppy mode" (in progress))
--harmony_unicode_regexps (enable "harmony unicode regexps" (in progress))
--harmony_reflect (enable "harmony Reflect API" (in progress))
--harmony_destructuring (enable "harmony destructuring" (in progress))
--harmony_default_parameters (enable "harmony default parameters" (in progress))
--harmony_sharedarraybuffer (enable "harmony sharedarraybuffer" (in progress))
--harmony_atomics (enable "harmony atomics" (in progress))
--harmony_simd (enable "harmony simd" (in progress))
--harmony_array_includes (enable "harmony Array.prototype.includes")
--harmony_tostring (enable "harmony toString")
--harmony_concat_spreadable (enable "harmony isConcatSpreadable")
--harmony_rest_parameters (enable "harmony rest parameters")
--harmony_sloppy (enable "harmony features in sloppy mode")
--harmony_arrow_functions (enable "harmony arrow functions")
--harmony_new_target (enable "harmony new.target")
--harmony_object_observe (enable "harmony Object.observe")
--harmony_spreadcalls (enable "harmony spread-calls")
--harmony_spread_arrays (enable "harmony spread in array literals")
--harmony_object (enable "harmony Object methods")

The flag you need, --harmony_destructuring, was added in Node 4.1. Currently, you'll need to pass the --harmony_destructuring flag to enable the feature:

$ node --harmony_destructuring
> var {foo} = {foo: 'bar'};
undefined
> foo
'bar'

edited Jan 16, 2017 at 14:43

mikemaccana

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answered Jun 29, 2013 at 11:29

Laurent Perrin

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2 Comments

user663031 Over a year ago

@BrianMcCutchon Without var, you'll need to do ({foo} = {foo: 'bar}) to prevent the leading { from being interpreted as starting a block. That's the same in any implementation.

Brian McCutchon Over a year ago

@torazaburo Interesting, hadn't thought of that. You're supposed to be able to omit the var/let when destructuring arrays, though, but that doesn't seem to work in node yet.

birnbaum · Accepted Answer · 2016-05-09 11:26:16Z

15

The lately released node.js v6 is using V8 version 5.0 which is supporting 93% of ES2015 language features (even 96% in v6.1).

Destructuring assignments can now be considered stable and can be used without any flags.

answered May 9, 2016 at 11:26

birnbaum

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Comments

Dan Dascalescu · Accepted Answer · 2015-10-02 23:45:09Z

10

The ES6 compatibility table shows that destructuring isn't supported in either Chrome 45, or Node v4.

answered Oct 2, 2015 at 23:45

Dan Dascalescu

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4 Comments

Ahmed Fasih Over a year ago

Even with node --harmony_destructuring 😓

kernel Over a year ago

In Node v5.0.0 it works with node --harmony_destructuring. I don't know about v4.

Alex Rudenko Over a year ago

works for me in node 4.2.2 with --harmony_destructuring

machineghost Over a year ago

As of the latest Chrome (49) destructuring is now supported. As long as you stick to Chrome or Node (with the appropriate flags) you can now use just about all of ES6 without even needing a transpiler like Babel.

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