Node.js console.log(object) prints empty object

Question

I'm curious about the way Node.js prints objects through console.log(object).

I have the following code (from Learning Javascript Design Patterns book) under a file constructor.js

var defineProp = function(obj, key, value){
    var config = {
        value: value, 
        writable: true,
        configurable: true
    };
    Object.defineProperty(obj, key, config ); 
}

var person = Object.create(Object.prototype);


defineProp(person, "car", "Delorean"); 
defineProp(person, "dateOfBirth", "1981"); 
defineProp(person, "hasBeard", false); 

console.log(person); //This prints {} in Node.js

Running with that code with >node constructor.js prints an empty object. Chrome however, prints what I would expect if I run the code inside an HTML file.

console.log(person); //Chrome prints Object {car: "Delorean", dateOfBirth: "1981", hasBeard: false}

Note: I can still print the attributes (such as console.log(person.car)) under Node, just not the object itself (such as console.log(person))

Why is this? Do Chrome and Node use separate prototypes for the console object, even though they share the same javascript engine?

Not sure why they're different, but if you add enumerable: true to the config object the properties will print in node.js. — JohnnyHK
– JohnnyHK, Commented Oct 5, 2015 at 4:32
Possible duplicate of View methods of Node.js String.prototype? — Qantas 94 Heavy
– Qantas 94 Heavy, Commented Oct 5, 2015 at 4:32
By default, properties created with defineProperty() are not enumerable. So, perhaps node.js is only showing you enumerable properties and Chrome shows non-enumerable properties. console.log() is not a something specified in a standard and it is a host object, not official part of the Javascript language so different environments may have different behaviors. — jfriend00
– jfriend00, Commented Oct 5, 2015 at 4:35
The console.log in node is very different to the one in Chrome. First, node prints to stdout so its console.log had to be re-written to support streams. Which means from the very beginning node wasn't using the same console.log as Chrome. Second, from version 0.6 onward node's console.log is synchronous (vs Chrome's asynchronous) because people expected to see the last console.log they printed before their servers crash. Not being synchronous made it very difficult to debug crashing servers because the cause of the crash wouldn't be logged before node exits — slebetman
– slebetman, Commented Oct 5, 2015 at 4:41
@slebetman node's console.log() is only synchronous when stdout is redirected to a file. Otherwise it is always asynchronous on all platforms. There are already several issues on node's github issue tracker about that. — mscdex
– mscdex, Commented Oct 5, 2015 at 4:59

mscdex · Accepted Answer · 2015-10-05 05:07:13Z

7

console.log() in node utilizes util.inspect(), which uses Object.keys() on objects, which returns only own enumerable properties. Also, by default, Object.defineProperty() sets enumerable: false if you do not explicitly set it to true.

answered Oct 5, 2015 at 5:07

mscdex

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