Enable Harmony Proxies in nodejs

Question

Is it possible to enable EcmaScript 6 Harmony Proxies in nodejs? If so, what are the pros and cons? And is there any documentation on how to use them? Thanks !

Answer 1

Proxy is now available natively in Node versions >= 6.

Answer 2

Invoking node with node --harmony-proxies should do the trick.

Pros: proxies are a very powerful feature when you really need them.

Cons: proxies are a much too powerful feature when you don't need them (which should be most of the time). Also, the implementation should still be regarded experimental.

As for documentation, all there really is atm is the Harmony wiki, in particular this page, which reflects the current implementation of proxies in V8 (and thus node):

http://wiki.ecmascript.org/doku.php?id=harmony:proxies

Answer 3

You can use pimped-proxy which a lightweight implementation of proxies, making declaration easier and ES5 compatible. Unlike the native Proxy, it can only proxy properties known at creation time.

https://github.com/Boulangerie/pimped-proxy

Answer 4

i recommend harmony-reflect, which makes it easy to e.g. set up get/set traps:

UPDATE careful, below is CoffeeScript

require 'harmony-reflect'

handler =

  get: ( target, name ) ->
    console.log 'get' name
    return target[ name ]

  set: ( target, name, value ) ->
    console.log 'set' name
    target[ '%is-clean' ] = no if value isnt target[ name ]
    if value is undefined then delete target[ name ]
    else                       target[ name ] = value
    return value

clean = ( x ) ->
  x[ '%is-clean' ] = yes
  return x

p = Proxy {}, handler
p[ 'a' ] = 1
p[ 'b' ] = undefined
console.log p[ 'a' ], p[ 'b' ]
console.log "c" of p, p[ 'c' ]
console.log p
clean p
p[ 'a' ] = 1
console.log p
p[ 'a' ] = 42
console.log p

the above is the inceptive code to do 'transparent object persistence' in JavaScript. using harmony-reflect, it becomes trivial to make it so that all get and set actions on an object get intercepted—in this demo, we set an %is-clean attribute so we can test whether object members have been changed, and we also delete members that have been set to undefined.

Answer 5

Harmony Proxies won't work all that well for nodejs because they're effectively synchronous type function calls. That is, you can't implement a proxy method that's async.

See this GitHub repository for examples: https://github.com/mschwartz/SilkJS-Harmony