Proxies: console.log uses overridden proxy methods by default #12453

Activity

1. addaleax

   added

   utilIssues and PRs related to the built-in util module.Issues and PRs related to the built-in util module.

   on Apr 16, 2017
2. addaleax commented on Apr 16, 2017

   

   addaleax

   on Apr 16, 2017

   Member

   More actions

   Just fyi, util.inspect (and console.dir indirectly too) has a showProxy option that lets you enable displaying the proxy itself, see https://nodejs.org/api/util.html#util_util_inspect_object_options.

   But I see your point, and I’m not sure whether this should be a bug or not myself. What’s the alternative to passing the error along? Just defaulting to displaying the Proxy target doesn’t seem quite right…
3. ace-n commented on Apr 16, 2017

   

   ace-n

   on Apr 16, 2017

   Last edited by ace-n

   Author

   More actions

   To be honest, it makes sense to me that console.log should respect the Proxy (and, as you said, pass the error along). But it doesn't seem like it does so universally:

   'use strict';
   
   const handler = {
       get: function(target, prop) {
         return target[prop] + "baz";
       }
   };
   const sandbox = new Proxy({foo: 'bar'}, handler);
   console.log(sandbox);
   console.log(sandbox.foo);
   

   { foo: 'bar' } // should this be { foo: 'barbaz' }?
   barbaz
   

   Perhaps this is a question for the v8 folks?

   👍React with 👍1Reacted by Daniel Bayley
4. addaleax commented on Apr 16, 2017

   

   addaleax

   on Apr 16, 2017

   Member

   More actions

   That latter behaviour is because util.inspect uses Object.getOwnPropertyDescriptor to get the value, and in your example the proxy doesn’t provide that trap.

   (Ironically, one of the reasons util.inspect does that is to avoid getters that might throw errors. 😄)
5. ace-n commented on Apr 16, 2017

   

   ace-n

   on Apr 16, 2017

   Last edited by ace-n

   Author

   More actions

   Here's an example with the trap added:

   'use strict';
   
   const handler = {
       get: function(target, prop) {
         return (target && target[prop] && typeof target[prop] == 'string') ?
         	target[prop] + "baz" :
         	target[prop];
       },
       getOwnPropertyDescriptor: function(target, prop) {
         let a = Object.getOwnPropertyDescriptor(target, prop);
         if (a)
         	a.value = this.get(target, prop);
         return a;
       }
   };
   const sandbox = new Proxy({foo: 'bar'}, handler);
   console.log(sandbox);
   console.log(sandbox.foo);
   

   { foo: 'barbaz' }
   barbaz
   

   At first glance, it seems like everything is working correctly in this example (that doesn't involve error throwing). Perhaps this is just an eccentricity of Node or even Javascript itself? (I'm not sure if the ECMA specification has anything to say about this.)
6. TimothyGu commented on Apr 17, 2017

   

   TimothyGu

   on Apr 17, 2017

   Member

   More actions

   There are really no consensus on what console.log should do in this instance.

   The way Chrome handles it is always displaying the proxied target in the short one-line view, and providing more information about the proxy once you expand it:

   
   

   Firefox on the other hand always displays the proxied values, and does not allow introspection of the internal slots of the proxy object:

   

   And in case of thrown errors, it just says "Error":

   

   FWIW the Console Standard does not say anything about the possibility of throwing either.
7. Trott commented on Aug 2, 2017

   

   Trott

   on Aug 2, 2017

   Member

   More actions

   Should this remain open?
8. BridgeAR commented on Aug 28, 2017

   

   BridgeAR

   on Aug 28, 2017

   Member

   More actions

   As far as I see it everything is working as it should. I am closing this therefore.
9. BridgeAR

   closed this as completedon Aug 28, 2017
10. bnoordhuis commented on Aug 29, 2017

    

    bnoordhuis

    on Aug 29, 2017

    Member

    More actions

    Linking to #13784 - it's related in the sense that we currently lack a safe way to inspect JS values.